[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (RFC 3921) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 RFC 6121

Network Working Group                                     P. Saint-Andre
Internet-Draft                                                     Cisco
Obsoletes: 3921 (if approved)                             March 31, 2010
Intended status: Standards Track
Expires: October 2, 2010


Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and
                                Presence
                       draft-ietf-xmpp-3921bis-06

Abstract

   This document defines extensions to core features of the Extensible
   Messaging and Presence Protocol (XMPP) that provide basic instant
   messaging (IM) and presence functionality in conformance with RFC
   2779.

   This document obsoletes RFC 3921.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on October 2, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




Saint-Andre              Expires October 2, 2010                [Page 1]

Internet-Draft                   XMPP IM                      March 2010


   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   6
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   6
     1.2.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Functional Summary  . . . . . . . . . . . . . . . . . . .   8
     1.4.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   9
     1.5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . .   9
     1.6.  Discussion Venue  . . . . . . . . . . . . . . . . . . . .  10
   2.  Managing the Roster . . . . . . . . . . . . . . . . . . . . .  10
     2.1.  Syntax and Semantics  . . . . . . . . . . . . . . . . . .  10
       2.1.1.  Ver Attribute . . . . . . . . . . . . . . . . . . . .  10
       2.1.2.  Roster Items  . . . . . . . . . . . . . . . . . . . .  10
         2.1.2.1.  Ask Attribute . . . . . . . . . . . . . . . . . .  11
         2.1.2.2.  Jid Attribute . . . . . . . . . . . . . . . . . .  11
         2.1.2.3.  Name Attribute  . . . . . . . . . . . . . . . . .  11
         2.1.2.4.  Subscription Attribute  . . . . . . . . . . . . .  11
         2.1.2.5.  Group Element . . . . . . . . . . . . . . . . . .  11
       2.1.3.  Roster Get  . . . . . . . . . . . . . . . . . . . . .  12
       2.1.4.  Roster Set  . . . . . . . . . . . . . . . . . . . . .  12
       2.1.5.  Roster Push . . . . . . . . . . . . . . . . . . . . .  13
       2.1.6.  Roster Result . . . . . . . . . . . . . . . . . . . .  13
       2.1.7.  Subscription Attribute  . . . . . . . . . . . . . . .  14
     2.2.  Retrieving the Roster on Login  . . . . . . . . . . . . .  15
     2.3.  Adding a Roster Item  . . . . . . . . . . . . . . . . . .  16
       2.3.1.  Request . . . . . . . . . . . . . . . . . . . . . . .  16
       2.3.2.  Success Case  . . . . . . . . . . . . . . . . . . . .  17
       2.3.3.  Error Cases . . . . . . . . . . . . . . . . . . . . .  18
     2.4.  Updating a Roster Item  . . . . . . . . . . . . . . . . .  22
       2.4.1.  Request . . . . . . . . . . . . . . . . . . . . . . .  22
       2.4.2.  Success Case  . . . . . . . . . . . . . . . . . . . .  24
       2.4.3.  Error Cases . . . . . . . . . . . . . . . . . . . . .  24
     2.5.  Deleting a Roster Item  . . . . . . . . . . . . . . . . .  24
       2.5.1.  Request . . . . . . . . . . . . . . . . . . . . . . .  24
       2.5.2.  Success Case  . . . . . . . . . . . . . . . . . . . .  24
       2.5.3.  Error Cases . . . . . . . . . . . . . . . . . . . . .  25
     2.6.  Roster Versioning . . . . . . . . . . . . . . . . . . . .  25



Saint-Andre              Expires October 2, 2010                [Page 2]

Internet-Draft                   XMPP IM                      March 2010


       2.6.1.  Stream Feature  . . . . . . . . . . . . . . . . . . .  25
       2.6.2.  Request . . . . . . . . . . . . . . . . . . . . . . .  26
       2.6.3.  Success Case  . . . . . . . . . . . . . . . . . . . .  26
   3.  Managing Presence Subscriptions . . . . . . . . . . . . . . .  29
     3.1.  Requesting a Subscription . . . . . . . . . . . . . . . .  30
       3.1.1.  Client Generation of Outbound Subscription Request  .  30
       3.1.2.  Server Processing of Outbound Subscription Request  .  31
       3.1.3.  Server Processing of Inbound Subscription Request . .  33
       3.1.4.  Client Processing of Inbound Subscription Request . .  35
       3.1.5.  Server Processing of Outbound Subscription Approval .  35
       3.1.6.  Server Processing of Inbound Subscription Approval  .  37
     3.2.  Cancelling a Subscription . . . . . . . . . . . . . . . .  38
       3.2.1.  Client Generation of Subscription Cancellation  . . .  38
       3.2.2.  Server Processing of Outbound Subscription
               Cancellation  . . . . . . . . . . . . . . . . . . . .  39
       3.2.3.  Server Processing of Inbound Subscription
               Cancellation  . . . . . . . . . . . . . . . . . . . .  40
     3.3.  Unsubscribing . . . . . . . . . . . . . . . . . . . . . .  41
       3.3.1.  Client Generation of Unsubscribe  . . . . . . . . . .  41
       3.3.2.  Server Processing of Outbound Unsubscribe . . . . . .  41
       3.3.3.  Server Processing of Inbound Unsubscribe  . . . . . .  42
   4.  Exchanging Presence Information . . . . . . . . . . . . . . .  44
     4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  44
     4.2.  Initial Presence  . . . . . . . . . . . . . . . . . . . .  45
       4.2.1.  Client Generation of Initial Presence . . . . . . . .  45
       4.2.2.  Server Processing of Outbound Presence  . . . . . . .  45
       4.2.3.  Server Processing of Inbound Presence . . . . . . . .  46
       4.2.4.  Client Processing of Inbound Presence . . . . . . . .  46
     4.3.  Presence Probes . . . . . . . . . . . . . . . . . . . . .  46
       4.3.1.  Server Generation of Outbound Presence Probe  . . . .  47
       4.3.2.  Server Processing of Inbound Presence Probe . . . . .  48
     4.4.  Subsequent Presence Broadcast . . . . . . . . . . . . . .  50
       4.4.1.  Client Generation of Presence Broadcast . . . . . . .  51
       4.4.2.  Server Processing of Outbound Presence  . . . . . . .  51
       4.4.3.  Server Processing of Inbound Presence . . . . . . . .  52
       4.4.4.  Client Processing of Inbound Presence . . . . . . . .  53
     4.5.  Unavailable Presence  . . . . . . . . . . . . . . . . . .  53
       4.5.1.  Client Generation of Unavailable Presence . . . . . .  53
       4.5.2.  Server Processing of Outbound Unavailable Presence  .  54
       4.5.3.  Server Processing of Inbound Unavailable Presence . .  55
       4.5.4.  Client Processing of Inbound Unavailable Presence . .  56
     4.6.  Directed Presence . . . . . . . . . . . . . . . . . . . .  56
       4.6.1.  Client Generation of Directed Presence  . . . . . . .  57
       4.6.2.  Server Processing of Outbound Directed Presence . . .  57
       4.6.3.  Server Processing of Inbound Directed Presence  . . .  57
       4.6.4.  Client Processing of Inbound Directed Presence  . . .  58
     4.7.  Presence Syntax . . . . . . . . . . . . . . . . . . . . .  58
       4.7.1.  Type Attribute  . . . . . . . . . . . . . . . . . . .  58



Saint-Andre              Expires October 2, 2010                [Page 3]

Internet-Draft                   XMPP IM                      March 2010


       4.7.2.  Child Elements  . . . . . . . . . . . . . . . . . . .  59
       4.7.3.  Show Element  . . . . . . . . . . . . . . . . . . . .  59
       4.7.4.  Status Element  . . . . . . . . . . . . . . . . . . .  60
       4.7.5.  Priority Element  . . . . . . . . . . . . . . . . . .  61
       4.7.6.  Extended Content  . . . . . . . . . . . . . . . . . .  61
   5.  Exchanging Messages . . . . . . . . . . . . . . . . . . . . .  62
     5.1.  One-to-One Chat Sessions  . . . . . . . . . . . . . . . .  62
     5.2.  Message Syntax  . . . . . . . . . . . . . . . . . . . . .  63
       5.2.1.  To Attribute  . . . . . . . . . . . . . . . . . . . .  63
       5.2.2.  Type Attribute  . . . . . . . . . . . . . . . . . . .  64
       5.2.3.  Body Element  . . . . . . . . . . . . . . . . . . . .  65
       5.2.4.  Subject Element . . . . . . . . . . . . . . . . . . .  66
       5.2.5.  Thread Element  . . . . . . . . . . . . . . . . . . .  67
     5.3.  Extended Content  . . . . . . . . . . . . . . . . . . . .  68
   6.  Exchanging IQ Stanzas . . . . . . . . . . . . . . . . . . . .  69
   7.  A Sample Session  . . . . . . . . . . . . . . . . . . . . . .  69
   8.  Server Rules for Processing XML Stanzas . . . . . . . . . . .  77
     8.1.  No Such User  . . . . . . . . . . . . . . . . . . . . . .  77
     8.2.  Full JID at Local Domain  . . . . . . . . . . . . . . . .  77
       8.2.1.  Resource Matches  . . . . . . . . . . . . . . . . . .  77
       8.2.2.  No Resource Matches . . . . . . . . . . . . . . . . .  78
     8.3.  Bare JID at Local Domain  . . . . . . . . . . . . . . . .  78
       8.3.1.  Available or Connected Resources  . . . . . . . . . .  79
         8.3.1.1.  Message . . . . . . . . . . . . . . . . . . . . .  79
         8.3.1.2.  Presence  . . . . . . . . . . . . . . . . . . . .  80
         8.3.1.3.  IQ  . . . . . . . . . . . . . . . . . . . . . . .  80
       8.3.2.  No Available or Connected Resources . . . . . . . . .  80
         8.3.2.1.  Message . . . . . . . . . . . . . . . . . . . . .  80
         8.3.2.2.  Presence  . . . . . . . . . . . . . . . . . . . .  81
         8.3.2.3.  IQ  . . . . . . . . . . . . . . . . . . . . . . .  81
     8.4.  Remote Domain . . . . . . . . . . . . . . . . . . . . . .  81
   9.  Handling of URIs  . . . . . . . . . . . . . . . . . . . . . .  82
   10. Internationalization Considerations . . . . . . . . . . . . .  83
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  83
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  84
     12.1. Instant Messaging SRV Protocol Label Registration . . . .  84
     12.2. Presence SRV Protocol Label Registration  . . . . . . . .  84
   13. Conformance Requirements  . . . . . . . . . . . . . . . . . .  84
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  87
     14.1. Normative References  . . . . . . . . . . . . . . . . . .  87
     14.2. Informative References  . . . . . . . . . . . . . . . . .  88
   Appendix A.  Subscription States  . . . . . . . . . . . . . . . .  90
     A.1.  Defined States  . . . . . . . . . . . . . . . . . . . . .  91
     A.2.  Server Processing of Outbound Presence Subscription
           Stanzas . . . . . . . . . . . . . . . . . . . . . . . . .  92
       A.2.1.  Subscribe . . . . . . . . . . . . . . . . . . . . . .  92
       A.2.2.  Unsubscribe . . . . . . . . . . . . . . . . . . . . .  93
       A.2.3.  Subscribed  . . . . . . . . . . . . . . . . . . . . .  93



Saint-Andre              Expires October 2, 2010                [Page 4]

Internet-Draft                   XMPP IM                      March 2010


       A.2.4.  Unsubscribed  . . . . . . . . . . . . . . . . . . . .  94
     A.3.  Server Processing of Inbound Presence Subscription
           Stanzas . . . . . . . . . . . . . . . . . . . . . . . . .  94
       A.3.1.  Subscribe . . . . . . . . . . . . . . . . . . . . . .  95
       A.3.2.  Unsubscribe . . . . . . . . . . . . . . . . . . . . .  95
       A.3.3.  Subscribed  . . . . . . . . . . . . . . . . . . . . .  96
       A.3.4.  Unsubscribed  . . . . . . . . . . . . . . . . . . . .  97
   Appendix B.  Blocking Communication . . . . . . . . . . . . . . .  98
   Appendix C.  vCards . . . . . . . . . . . . . . . . . . . . . . .  98
   Appendix D.  XML Schemas  . . . . . . . . . . . . . . . . . . . .  98
     D.1.  jabber:client . . . . . . . . . . . . . . . . . . . . . .  98
     D.2.  jabber:server . . . . . . . . . . . . . . . . . . . . . . 103
     D.3.  jabber:iq:roster  . . . . . . . . . . . . . . . . . . . . 107
   Appendix E.  Differences From RFC 3921  . . . . . . . . . . . . . 108
   Appendix F.  Copying Conditions . . . . . . . . . . . . . . . . . 109
   Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . 110


































Saint-Andre              Expires October 2, 2010                [Page 5]

Internet-Draft                   XMPP IM                      March 2010


1.  Introduction

1.1.  Overview

   The Extensible Messaging and Presence Protocol (XMPP) is an
   application profile of the Extensible Markup Language [XML] for
   streaming XML data in close to real time between any two (or more)
   network-aware entities.  XMPP is typically used to exchange messages,
   share presence information, and engage in structured request-response
   interactions.  The core features of XMPP defined in [XMPP-CORE]
   provide the building blocks for many types of near-real-time
   applications, which can be layered on top of the core by sending
   application-specific data qualified by particular XML namespaces
   (refer to [XML-NAMES]).  This document defines XMPP extensions that
   provide the basic functionality expected of an instant messaging (IM)
   and presence application as defined in [IMP-REQS].

   As a result of extensive implementation and deployment experience
   with XMPP since 2004, as well as more formal interoperability testing
   carried out under the auspices of the XMPP Standards Foundation
   (XSF), this document reflects consensus from the XMPP developer
   community regarding XMPP's basic instant messaging and presence
   features.  In particular, this document incorporates the following
   backward-compatible changes from RFC 3921:

   o  Incorporated corrections and errata
   o  Added examples throughout
   o  Clarified and more completely specified matters that were
      underspecified
   o  Removed the protocol for session establishment, which was deemed
      unnecessary
   o  Modified error handling related to presence stanzas to more
      seamlessly repair lack of synchronization in subscription states
      between rosters located at different servers
   o  Added optional server support for pre-approved presence
      subscriptions
   o  Added optional 'parent' attribute to <thread/> element
   o  Transferred documentation for the communications blocking protocol
      from this specification to a separate specification

   Therefore, this document defines the basic instant messaging and
   presence features of XMPP 1.0, thus obsoleting RFC 3921.

1.2.  Requirements

   Traditionally, instant messaging applications have combined the
   following factors:




Saint-Andre              Expires October 2, 2010                [Page 6]

Internet-Draft                   XMPP IM                      March 2010


   1.  The central point of focus is a list of one's contacts or
       "buddies" (in XMPP this list is called a ROSTER).
   2.  The purpose of using such an application is to exchange
       relatively brief text messages with particular contacts in close
       to real time -- often relatively large numbers of such messages
       in rapid succession, in the form of a one-to-one CHAT SESSION as
       described under Section 5.1.
   3.  The catalyst for exchanging messages is PRESENCE -- i.e.,
       information about the network availability of particular contacts
       (thus knowing who is online and available for a one-to-one chat
       session).
   4.  Presence information is provided only to contacts that one has
       authorized by means of an explicit agreement called a PRESENCE
       SUBSCRIPTION.

   Thus at a high level this document assumes that a user must be able
   to complete the following use cases:

   o  Manage items in one's contact list
   o  Exchange messages with one's contacts
   o  Exchange presence information with one's contacts
   o  Manage presence subscriptions to and from one's contacts

   Detailed definitions of these functionality areas are contained in
   RFC 2779 [IMP-REQS], and the interested reader is referred to that
   document regarding the requirements addressed herein.  While the XMPP
   instant messaging and presence extensions specified herein meet the
   requirements of RFC 2779, they were not designed explicitly with that
   specification in mind, since the base protocol evolved through an
   open development process within the Jabber open-source community
   before RFC 2779 was written.  Although XMPP protocol extensions
   addressing many other functionality areas have been defined in the
   XMPP Standards Foundation's XEP series (e.g., multi-user text chat as
   specified in [XEP-0045]), such extensions are not specified in this
   document because they are not mandated by RFC 2779.

      Note: RFC 2779 stipulates that presence services must be separable
      from instant messaging services and vice-versa; i.e., it must be
      possible to use the protocol to provide a presence service, an
      instant messaging service, or both.  Although the text of this
      document assumes that implementations and deployments will want to
      offer a unified instant messaging and presence service, there is
      no requirement that a service must offer both a presence service
      and an instant messaging service, and the protocol makes it
      possible to offer separate and distinct services for presence and
      for instant messaging.  (For example, a presence-only service
      could return a <service-unavailable/> stanza error if a client
      attempt to send a <message/> stanza.)



Saint-Andre              Expires October 2, 2010                [Page 7]

Internet-Draft                   XMPP IM                      March 2010


1.3.  Functional Summary

   This non-normative section provides a developer-friendly, functional
   summary of XMPP-based instant messaging and presence features;
   consult the sections that follow for a normative definition of these
   features.

   [XMPP-CORE] specifies how an XMPP client connects to an XMPP server.
   In particular, it specifies the preconditions that must be fulfilled
   before a client is allowed to send XML stanzas (the basic unit of
   meaning in XMPP) to other entities on an XMPP network.  These
   preconditions comprise negotiation of the XML stream and include XML
   stream establishment, optional channel encryption via Transport Layer
   Security [TLS], mandatory authentication via Simple Authentication
   and Security Layer [SASL], and binding of a resource to the stream
   for client addressing.  The reader is referred to [XMPP-CORE] for
   details regarding these preconditions, and knowledge of [XMPP-CORE]
   is assumed herein.

      Note: [RFC3921] specified one additional precondition: formal
      establishment of an instant messaging and presence session.
      Implementation and deployment experience has shown that this
      additional step is unnecessary.  However, for backward
      compatibility an implementation SHOULD still offer that feature
      and note in the stream feature that negotiation of the feature is
      discretionary (via the <optional/> child element).  This enables
      older software to connect while saving newer software to skip a
      round trip.

   Upon fulfillment of the preconditions specified in [XMPP-CORE], an
   XMPP client has a long-lived XML stream with an XMPP server, which
   enables the user controlling that client to send and receive a
   potentially unlimited number of XML stanzas over the stream.  Such a
   stream can be used to exchange messages, share presence information,
   and engage in structured request-response interactions in close to
   real time.  After negotiation of the XML stream, the typical flow for
   an instant messaging and presence session is as follows:

   1.  Retrieve one's roster.  (See Section 2.2.)
   2.  Send initial presence to the server for broadcasting to all
       subscribed contacts, thus "going online" from the perspective of
       XMPP communication.  (See Section 4.2.)
   3.  Exchange messages, manage presence subscriptions, perform roster
       updates, and in general process and generate other XML stanzas
       with particular semantics throughout the life of the session.
       (See Section 5, Section 3, Section 2, and Section 6.)





Saint-Andre              Expires October 2, 2010                [Page 8]

Internet-Draft                   XMPP IM                      March 2010


   4.  Terminate the session when desired by sending unavailable
       presence and closing the underlying XML stream.  (See
       Section 4.5.)

1.4.  Conventions

   This document inherits the terminology defined in [XMPP-CORE].

   The following keywords are to be interpreted as described in [TERMS]:
   "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD",
   "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

   For convenience, this document employs the term "user" to refer to
   the owner of an XMPP account; however, account owners need not be
   human persons and can be bots, devices, or other non-human
   applications.

   Following the "XML Notation" used in [IRI] to represent characters
   that cannot be rendered in ASCII-only documents, some examples in
   this document use the form "&#x...." as a notational device to
   represent Unicode characters (e.g., the string "&#x0159;" stands for
   the Unicode character LATIN SMALL LETTER R WITH CARON).

   In examples, lines have been wrapped for improved readability,
   "[...]" means elision, and the following prepended strings are used
   (these prepended strings are not to be sent over the wire):

   o  C: = client
   o  CC: = contact's client
   o  CS: = contact's server
   o  S: = server
   o  UC: = user's client
   o  US: = user's server

1.5.  Acknowledgements

   The editor of this document finds it impossible to appropriately
   acknowledge the many individuals who have provided comments regarding
   the protocols defined herein.  However, thanks are due to those who
   have who have provided implementation feedback, bug reports, requests
   for clarification, and suggestions for improvement since the
   publication of the RFC this document supersedes.  The editor has
   endeavored to address all such feedback, but is solely responsible
   for any remaining errors and ambiguities.

   Portions of the text about roster versioning has been borrowed from
   [XEP-0237].




Saint-Andre              Expires October 2, 2010                [Page 9]

Internet-Draft                   XMPP IM                      March 2010


1.6.  Discussion Venue

   [[ RFC Editor: please remove this section. ]]

   The document editor and the broader XMPP developer community welcome
   discussion and comments related to the topics presented in this
   document.  The primary and preferred venue is the <xmpp@ietf.org>
   mailing list, for which archives and subscription information are
   available at <https://www.ietf.org/mailman/listinfo/xmpp>.  Related
   discussions often occur on the <standards@xmpp.org> mailing list, for
   which archives and subscription information are available at
   <http://mail.jabber.org/mailman/listinfo/standards>.


2.  Managing the Roster

   In XMPP, one's roster contains any number of specific contacts.  A
   user's roster is stored by the user's server on the user's behalf so
   that the user can access roster information from any resource.
   Because the user's roster can contain confidential data, the server
   MUST restrict access to this data so that only authorized entities
   (typically limited to the account owner) are able to retrieve,
   modify, or delete it.

2.1.  Syntax and Semantics

   Rosters are managed using IQ stanzas, specifically by means of a
   <query/> child element qualified by the 'jabber:iq:roster' namespace.
   The detailed syntax and semantics are defined in the following
   sections.

2.1.1.  Ver Attribute

   The 'ver' attribute is a string that identifies a particular version
   of the roster information.  The value MUST be generated only by the
   server and MUST be treated by the client as opaque.  The server can
   use any appropriate method for generating the version ID, such as a
   hash of the roster data or a strictly-increasing sequence number.

   Inclusion of the 'ver' attribute is RECOMMENDED.

   Use of the 'ver' attribute is described more fully under Section 2.6.

2.1.2.  Roster Items

   The <query/> element MAY contain one or more <item/> children, each
   describing a unique ROSTER ITEM or "contact".




Saint-Andre              Expires October 2, 2010               [Page 10]

Internet-Draft                   XMPP IM                      March 2010


   The syntax of the <item/> element is described in the following
   sections.

2.1.2.1.  Ask Attribute

   The 'ask' attribute is used to specify certain subscription sub-
   states; for details, see Section 3.1.2.

   Inclusion of the 'ask' attribute is OPTIONAL.

2.1.2.2.  Jid Attribute

   The 'jid' attribute specifies the Jabber Identifier (JID) that
   uniquely identifies the roster item.

   Inclusion of the 'jid' attribute is REQUIRED.

2.1.2.3.  Name Attribute

   The 'name' attribute specifies the "handle" to be associated with the
   JID, as determined by the user (not the contact).  Although the value
   of the 'name' attribute MAY have meaning to a human user, it is
   opaque to the server.  However, the 'name' attribute MAY be used by
   the server for matching purposes within the context of various XMPP
   extensions, in which case the values MUST be compared only after
   application of the Resourceprep profile of stringprep as defined in
   [XMPP-CORE].

   Inclusion of the 'name' attribute is OPTIONAL.

2.1.2.4.  Subscription Attribute

   The 'subscription' attribute is OPTIONAL; see Section 2.1.7.

   Inclusion of the 'subscription' attribute is OPTIONAL.

2.1.2.5.  Group Element

   The <group/> child element specifies a category or "bucket" into
   which the roster item is to be grouped by a client.  An <item/>
   element MAY contain more than one <group/> element, so that roster
   groups are not exclusive.  Although the XML character data of the
   <group/> element MAY have meaning to a human user, it is opaque to
   the server.  However, the <group/> element MAY be used by the server
   for matching purposes within the context of various XMPP extensions,
   in which case the data MUST be compared only after application of the
   Resourceprep profile of stringprep as defined in [XMPP-CORE].




Saint-Andre              Expires October 2, 2010               [Page 11]

Internet-Draft                   XMPP IM                      March 2010


   Inclusion of the <group/> child element is OPTIONAL.

2.1.3.  Roster Get

   A ROSTER GET is a client's request for the server to send the roster;
   syntactically it is an IQ stanza of type "get" sent from client to
   server and containing a <query/> element qualified by the 'jabber:iq:
   roster' namespace, where the <query/> element MUST NOT contain any
   <item/> child elements.

   C: <iq from='juliet@example.com/balcony'
          id='rg1'
          type='get'>
       <query xmlns='jabber:iq:roster'/>
     </iq>

   The expected outcome of sending a roster get is for the server to
   return a roster result.

2.1.4.  Roster Set

   A ROSTER SET is a client's request for the server to modify (i.e.,
   create, update, or delete) a roster item; syntactically it is an IQ
   stanza of type "set" sent from client to server and containing a
   <query/> element qualified by the 'jabber:iq:roster' namespace.

   The following rules apply to roster sets:

   1.  The <query/> element MUST contain one and only one <item/>
       element.
   2.  The server MUST ignore any value of the 'subscription' attribute
       other than "remove" (see Section 2.1.7).
   3.  The server MUST ignore any 'to' address specified on the IQ
       stanza and MUST handle the IQ stanza as if it included no 'to'
       attribute.

   C: <iq from='juliet@example.com/balcony'
          id='rs1'
          type='set'>
       <query xmlns='jabber:iq:roster'>
         <item jid='nurse@example.com'/>
       </query>
     </iq>








Saint-Andre              Expires October 2, 2010               [Page 12]

Internet-Draft                   XMPP IM                      March 2010


2.1.5.  Roster Push

   A ROSTER PUSH is a newly created, updated, or deleted roster item
   that is sent from the server to the client; syntactically it is an IQ
   stanza of type "set" sent from server to client and containing a
   <query/> element qualified by the 'jabber:iq:roster' namespace.

   The following rules apply to roster pushes:

   1.  The <query/> element in a roster push MUST contain one and only
       one <item/> element.
   2.  A receiving client MUST ignore the stanza unless it has no 'from'
       attribute (i.e., implicitly from the user's bare JID) or it has a
       'from' attribute whose value matches the user's bare JID
       <user@domain>.

   S: <iq id='a78b4q6ha463'
          to='juliet@example.com/chamber'
          type='set'>
       <query xmlns='jabber:iq:roster'>
         <item jid='nurse@example.com'/>
       </query>
     </iq>

   As mandated by the semantics of the IQ stanza as defined in
   [XMPP-CORE], each resource that receives a roster push MUST reply
   with an IQ stanza of type "result" (or "error").

   C: <iq from='juliet@example.com/balcony'
          id='a78b4q6ha463'
          type='result'/>

   C: <iq from='juliet@example.com/chamber'
          id='a78b4q6ha463'
          type='result'/>

      Note: There is no error case for client processing of roster
      pushes; if the server receives an IQ of type "error" in response
      to a roster push it SHOULD ignore the error.

2.1.6.  Roster Result

   A ROSTER RESULT is the server's response to a roster get;
   syntactically it is an IQ stanza of type "result" sent from server to
   client and containing a <query/> element qualified by the 'jabber:iq:
   roster' namespace.

   The <query/> element in a roster result contains one <item/> element



Saint-Andre              Expires October 2, 2010               [Page 13]

Internet-Draft                   XMPP IM                      March 2010


   for each contact and therefore can contain more than one <item/>
   element.

   S: <iq id='rg1'
          to='juliet@example.com/chamber'
          type='result'>
       <query xmlns='jabber:iq:roster' ver='ver7'>
         <item jid='nurse@example.com'/>
         <item jid='romeo@example.net'/>
       </query>
     </iq>

   If there are no contacts in the roster, then the server MUST return
   an IQ-result containing a child <query/> element that in turn
   contains no <item/> children (e.g., the server MUST NOT return an
   empty <iq/> stanza element).

   S: <iq to='juliet@example.com/chamber'
          id='roster_result'
          type='result'>
       <query xmlns='jabber:iq:roster' ver='ver9'/>
     </iq>

2.1.7.  Subscription Attribute

   The state of the presence subscription in relation to a roster item
   is captured in the 'subscription' attribute of the <item/> element.
   Allowable subscription-related values for this attribute are:

   o  "none" -- the user does not have a subscription to the contact's
      presence, and the contact does not have a subscription to the
      user's presence; this is the default value, so if the subscription
      attribute is not included then the state is to be understood as
      "none"
   o  "to" -- the user has a subscription to the contact's presence, but
      the contact does not have a subscription to the user's presence
   o  "from" -- the contact has a subscription to the user's presence,
      but the user does not have a subscription to the contact's
      presence
   o  "both" -- both the user and the contact have subscriptions to each
      other's presence (also called a "mutual subscription")

   In a roster result, the client MUST ignore values of the
   'subscription' attribute other than "none", "to", "from", or "both".

   In a roster push, the client MUST ignore values of the 'subscription'
   attribute other than "none", "to", "from", "both", or "remove".




Saint-Andre              Expires October 2, 2010               [Page 14]

Internet-Draft                   XMPP IM                      March 2010


   In a roster set, the value of the 'subscription' attribute MAY be
   included with a value of "remove", which indicates that the item is
   to be removed from the roster; the server MUST ignore all values of
   the 'subscription' attribute other than "remove".

2.2.  Retrieving the Roster on Login

   Upon authenticating with a server and binding a resource (thus
   becoming a connected resource), a client SHOULD request the roster
   before sending initial presence (however, because receiving the
   roster is not necessarily desirable for all resources, e.g., a
   connection with limited bandwidth, the client's request for the
   roster is not mandatory).  After a connected resource sends initial
   presence (see Section 4.2), it is referred to as an available
   resource.  If a connected resource or available resource requests the
   roster, it is referred to as an INTERESTED RESOURCE.  The server MUST
   send roster pushes to all interested resources.

      Note: Presence subscription requests are sent to available
      resources, whereas the roster pushes associated with subscription
      state changes are sent to interested resources.  Therefore if a
      resource wishes to receive both subscription requests and roster
      pushes, it MUST both send initial presence and request the roster.

   A client requests the roster by sending a roster get over its stream
   to the server.

   C: <iq from='juliet@example.com/balcony'
          id='roster_1'
          type='get'>
        <query xmlns='jabber:iq:roster'/>
      </iq>



















Saint-Andre              Expires October 2, 2010               [Page 15]

Internet-Draft                   XMPP IM                      March 2010


   S: <iq id='roster_1'
          to='juliet@example.com/balcony'
          type='result'>
        <query xmlns='jabber:iq:roster' ver='ver11'>
          <item jid='romeo@example.net'
                name='Romeo'
                subscription='both'>
            <group>Friends</group>
          </item>
          <item jid='mercutio@example.com'
                name='Mercutio'
                subscription='from'/>
          <item jid='benvolio@example.net'
                name='Benvolio'
                subscription='both'/>
        </query>
      </iq>

   If the server cannot process the roster get, it MUST return an
   appropriate stanza error as described in [XMPP-CORE] (such as
   <service-unavailable/> if the roster namespace is not supported or
   <internal-server-error/> if the server experiences trouble processing
   or returning the roster).

2.3.  Adding a Roster Item

2.3.1.  Request

   At any time, a client can add an item to the roster.  This is done by
   sending a roster set containing a new item.

   C: <iq from='juliet@example.com/balcony'
          id='roster_2'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'>
            <group>Servants</group>
          </item>
        </query>
      </iq>

      Note: When a user adds a contact for the purpose of tracking the
      user's presence subscription to a contact, the user's client
      SHOULD send a presence subscription request to the contact before
      generating any roster set related to the contact.  This enables
      the user's server to enforce any policies relevant to presence
      subscriptions (e.g., a prohibition on presence subscriptions to



Saint-Andre              Expires October 2, 2010               [Page 16]

Internet-Draft                   XMPP IM                      March 2010


      full JIDs).  For details, see Section 3.

2.3.2.  Success Case

   If the server can successfully process the roster set (i.e., if none
   of the error cases occurs), it MUST create the roster item in
   persistent storage.

   The server MUST then return an IQ stanza of type "result" to the
   connected resource that sent the roster set.

   S: <iq id='roster_2'
          to='juliet@example.com/balcony'
          type='result'/>

   The server MUST also send a roster push containing the new roster
   item to all of the user's interested resources, including the
   resource that generated the roster set.

   S: <iq to='juliet@example.com/balcony'
          id='a78b4q6ha463'
          type='set'>
        <query xmlns='jabber:iq:roster' ver='ver13'>
          <item jid='nurse@example.com'
                name='Nurse'
                subscription='none'>
            <group>Servants</group>
          </item>
        </query>
      </iq>

   S: <iq to='juliet@example.com/chamber'
          id='a78b4q6ha464'
          type='set'>
        <query xmlns='jabber:iq:roster' ver='ver13'>
          <item jid='nurse@example.com'
                name='Nurse'
                subscription='none'>
            <group>Servants</group>
          </item>
        </query>
      </iq>

   As mandated by the semantics of the IQ stanza as defined in
   [XMPP-CORE], each resource that receives a roster push MUST reply
   with an IQ stanza of type "result" (or "error").





Saint-Andre              Expires October 2, 2010               [Page 17]

Internet-Draft                   XMPP IM                      March 2010


   C: <iq from='juliet@example.com/balcony'
          id='a78b4q6ha463'
          type='result'/>

   C: <iq from='juliet@example.com/chamber'
          id='a78b4q6ha464'
          type='result'/>

2.3.3.  Error Cases

   If the server cannot successfully process the roster set, it MUST
   return a stanza error.  The following error cases are defined
   (naturally, other stanza errors can occur, such as <internal-server-
   error/>).

   The server SHOULD return a <bad-request/> stanza error to the client
   if the roster set violates any of the following conditions:

   1.  The <query/> element contains more than one <item/> child
       element.
   2.  The <item/> element contains more than one <group/> element, but
       there are duplicate groups (where duplicates are determined using
       the Resourceprep profile of stringprep as defined in
       [XMPP-CORE]).

   The server SHOULD return a <not-acceptable/> stanza error to the
   client if the roster set violates any of the following conditions:

   1.  The value of the 'name' attribute is greater than a server-
       configured limit.
   2.  The XML character data of the <group/> element is of zero length.
   3.  The XML character data of the <group/> element is greater than a
       server-configured limit.

   Alternatively, the server MAY ignore the foregoing violations and
   process the roster set as best as possible (e.g., process only the
   first <item/> element, ignore duplicate <group/> elements, place the
   roster item in no group or a default group if the <group/> element is
   empty, and truncate 'name' attributes and <group/> elements that are
   too long).











Saint-Andre              Expires October 2, 2010               [Page 18]

Internet-Draft                   XMPP IM                      March 2010


   Error: Roster set contains more than one item

   C: <iq from='juliet@example.com/balcony'
          id='roster_3'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'>
            <group>Servants</group>
          </item>
          <item jid='mother@example.com'
                name='Mom'>
            <group>Family</group>
          </item>
        </query>
      </iq>

   S: <iq id='roster_3'
          to='juliet@example.com/balcony'
          type='error'>
       <error type='modify'>
         <bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
       </error>
     </iq>

   Error: Roster set contains item with oversized handle

   C: <iq from='juliet@example.com/balcony'
          id='roster_4'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='[ ... some-very-long-handle ... ]'>
            <group>Servants</group>
          </item>
        </query>
      </iq>

   S: <iq id='roster_4'
          to='juliet@example.com/balcony'
          type='error'>
        <error type='modify'>
          <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
        </error>
      </iq>






Saint-Andre              Expires October 2, 2010               [Page 19]

Internet-Draft                   XMPP IM                      March 2010


   Error: Roster set contains duplicate groups

   C: <iq from='juliet@example.com/balcony'
          id='roster_5'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'>
            <group>Servants</group>
            <group>Servants</group>
          </item>
        </query>
      </iq>

   S: <iq id='roster_5'
          to='juliet@example.com/balcony'
          type='error'>
        <error type='modify'>
          <bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
        </error>
      </iq>

   Error: Roster set contains empty group

   C: <iq from='juliet@example.com/balcony'
          id='roster_6'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'>
            <group></group>
          </item>
        </query>
      </iq>

   S: <iq id='roster_6'
          to='juliet@example.com/balcony'
          type='error'>
        <error type='modify'>
          <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
        </error>
      </iq>









Saint-Andre              Expires October 2, 2010               [Page 20]

Internet-Draft                   XMPP IM                      March 2010


   Error: Roster set contains oversized group

   C: <iq from='juliet@example.com/balcony'
          id='roster_7'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'>
            <group>[ ... some-very-long-group-name ... ]</group>
          </item>
        </query>
      </iq>

   S: <iq id='roster_7'
          to='juliet@example.com/balcony'
          type='error'>
        <error type='modify'>
          <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
        </error>
      </iq>

   The server MUST return a <not-allowed/> stanza error to the client if
   the value of the <item/> element's 'jid' attribute matches the bare
   JID <node@domain> portion of the <iq/> element's 'from' attribute
   (i.e., a JID MUST NOT be allowed to add itself to its own roster).

   Error: Roster set contains sender's JID

   C: <iq from='juliet@example.com/balcony'
          id='roster_8'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='juliet@example.com'/>
         </query>
       </iq>

   S: <iq id='roster_8'
          to='juliet@example.com/balcony'
          type='error'>
         <error type='cancel'>
           <not-allowed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
         </error>
       </iq>








Saint-Andre              Expires October 2, 2010               [Page 21]

Internet-Draft                   XMPP IM                      March 2010


2.4.  Updating a Roster Item

2.4.1.  Request

   Updating an existing roster item is done in the same way as adding a
   new roster item, i.e., by sending a roster set to the server.
   Because a roster item is atomic, the item MUST be updated exactly as
   provided in the roster set.

   There are several reasons why a client might update a roster item:

   1.  Adding a group
   2.  Deleting a group
   3.  Changing the handle
   4.  Deleting the handle

   Consider a roster item that is defined as follows:

       <item jid='romeo@example.net'
             name='Romeo'>
         <group>Friends</group>
       </item>

   The user who has this item in her roster might want to add the item
   to another group.

   C: <iq from='juliet@example.com/balcony'
          id='update_1'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'
                name='Romeo'>
            <group>Friends</group>
            <group>Lovers</group>
          </item>
        </query>
      </iq>

   The user might then want to remove the item from the original group.












Saint-Andre              Expires October 2, 2010               [Page 22]

Internet-Draft                   XMPP IM                      March 2010


   C: <iq from='juliet@example.com/balcony'
          id='update_2'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'
                name='Romeo'>
            <group>Lovers</group>
          </item>
        </query>
      </iq>

   The user might then want to change the handle for the item.

   C: <iq from='juliet@example.com/balcony'
          id='update_3'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'
                name='MyRomeo'>
            <group>Lovers</group>
          </item>
        </query>
      </iq>

   The user might then want to remove the handle altogether (note:
   including an empty 'name' attribute is equivalent to including no
   'name' attribute).

   C: <iq from='juliet@example.com/balcony'
          id='update_4'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'
                name=''>
            <group>Lovers</group>
          </item>
        </query>
      </iq>

   The user might then want to remove the item from all groups.

   C: <iq from='juliet@example.com/balcony'
          id='update_5'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'/>
        </query>
      </iq>



Saint-Andre              Expires October 2, 2010               [Page 23]

Internet-Draft                   XMPP IM                      March 2010


2.4.2.  Success Case

   As with adding a roster item, if the roster item can be successfully
   processed then the server MUST update the roster information in
   persistent storage, send a roster push to all of the user's
   interested resources, and send an IQ result to the initiating
   resource; for details, see Section 2.3.

2.4.3.  Error Cases

   The error cases described under Section 2.3.3 also apply to updating
   a roster item.

2.5.  Deleting a Roster Item

2.5.1.  Request

   At any time, a client can delete an item from his or her roster by
   sending a roster set and specifying the value of the 'subscription'
   attribute to be "remove".

   C: <iq from='juliet@example.com/balcony'
          id='delete_1'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com' subscription='remove'/>
        </query>
      </iq>

2.5.2.  Success Case

   As with adding a roster item, if the server can successfully process
   the roster set then it MUST update the roster information in
   persistent storage, send a roster push to all of the user's
   interested resources (with the 'subscription' attribute set to a
   value of "remove"), and send an IQ result to the initiating resource;
   for details, see Section 2.3.

   If the user has a presence subscription to the contact or the contact
   has a presence subscription to the user, the user's server MUST also
   generate a presence stanza of type "unsubscribe" (to unsubscribe from
   the contact's presence) or a presence stanza of type "unsubscribed"
   (to cancel the contact's subscription to the user), or both.








Saint-Andre              Expires October 2, 2010               [Page 24]

Internet-Draft                   XMPP IM                      March 2010


   S: <presence from='juliet@example.com'
                to='nurse@example.com'
                type='unsubscribe'/>

   S: <presence from='juliet@example.com'
                to='nurse@example.com'
                type='unsubscribed'/>

2.5.3.  Error Cases

   If the value of the 'jid' attribute specifies an item that is not in
   the roster, then the server MUST return an <item-not-found/> stanza
   error.

   Error: Roster item not found

   C: <iq from='juliet@example.com/balcony'
          id='delete_2'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='[ ... non-existent-jid ... ]'
                subscription='remove'/>
        </query>
      </iq>

   S: <iq id='delete_2'
          to='juliet@example.com/balcony'
          type='error'>
        <error type='modify'>
          <item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
        </error>
      </iq>

2.6.  Roster Versioning

2.6.1.  Stream Feature

   If a server supports roster versioning, then it MUST advertise the
   following stream feature during stream negotiation.

   <ver xmlns='urn:xmpp:features:rosterver'>
     <optional/>
   </ver>

   The roster versioning stream feature SHOULD always be voluntary
   (advertised by means of the <optional/> child element), not mandatory
   (advertised by means of the <required/> child element).




Saint-Andre              Expires October 2, 2010               [Page 25]

Internet-Draft                   XMPP IM                      March 2010


2.6.2.  Request

   If a client supports roster versioning and the server to which it has
   connected advertises support for roster versioning as described in
   the foregoing section, then the client MUST include the 'ver' element
   in its request for the roster.  If the server does not advertise
   support for roster versioning, the client MUST NOT include the 'ver'
   attribute.  If the client includes the 'ver' attribute in its roster
   get, it sets the attribute's value to the version ID associated with
   its last cache of the roster.

   C: <iq from='romeo@montague.lit/home'
          id='r1h3vzp7'
          to='romeo@montague.lit'
          type='get'>
        <query xmlns='jabber:iq:roster' ver='ver14'/>
      </iq>

   If the client has not yet cached the roster or the cache is lost or
   corrupted, but the client wishes to bootstrap the use of roster
   versioning, it MUST set the 'ver' attribute to the empty string
   (i.e., ver="").

   Naturally, if the client does not support roster versioning or does
   not wish to bootstrap the use of roster versioning, it will not
   include the 'ver' attribute.

2.6.3.  Success Case

   Whether or not the roster has been modified since the version ID
   enumerated by the client, the server MUST either return the complete
   roster as described under Section 2.1.6 (including a 'ver' attribute
   that signals the latest version) or return an empty IQ-result (thus
   indicating that any roster modifications will be sent via roster
   pushes, as described below).  In general, unless returning the
   complete roster would (1) use less bandwidth than sending individual
   roster pushes to the client (e.g., if the roster contains only a few
   items) or (2) the server cannot associate the version ID with any
   previous version it has on file, the server SHOULD send an empty IQ-
   result and then send the modifications (if any) via roster pushes.

   S: <iq from='romeo@montague.lit'
          id='r1h3vzp7'
          to='romeo@montague.lit/home'
          type='result'/>

   Note: This empty IQ-result is different from an empty <query/>
   element, thus disambiguating this usage from an empty roster.



Saint-Andre              Expires October 2, 2010               [Page 26]

Internet-Draft                   XMPP IM                      March 2010


   If the roster has not been modified since the version ID enumerated
   by the client, the server will simply not send any roster pushes to
   the client (until and unless some relevant event triggers a roster
   push during the lifetime of the client's session).

   If the roster has been modified since the version ID enumerated by
   the client, the server MUST then send one roster push to the client
   for each roster item that has been modified since the version ID
   enumerated by the client.  (We call a roster push that is sent for
   purposes of roster version synchronization an "interim roster push".)

      Definition: A ROSTER MODIFICATION is any modification to the
      roster data that would result in a roster push to a connected
      client.  Therefore internal states related to roster processing
      within the server that would not result in a roster push to a
      connected client do not necessitate a change to the version.



































Saint-Andre              Expires October 2, 2010               [Page 27]

Internet-Draft                   XMPP IM                      March 2010


   S: <iq from='romeo@montague.lit'
          id='ah382g67'
          to='romeo@montague.lit/home'
          type='set'>
        <query xmlns='jabber:iq:roster' ver='ver34'>
          <item jid='tybalt@shakespeare.lit' subscription='remove'/>
        </query>
      </iq>

   S: <iq from='romeo@montague.lit'
          id='b2gs90j5'
          to='romeo@montague.lit/home'
          type='set'>
        <query xmlns='jabber:iq:roster' ver='ver42'>
          <item jid='bill@shakespeare.lit' subscription='both'/>
        </query>
      </iq>

   S: <iq from='romeo@montague.lit'
          id='c73gs419'
          to='romeo@montague.lit/home'
          type='set'>
        <query xmlns='jabber:iq:roster' ver='ver72'>
          <item jid='nurse@shakespeare.lit'
                name='Nurse'
                subscription='to'>
            <group>Servants</group>
          </item>
        </query>
      </iq>

   S: <iq from='romeo@montague.lit'
          id='dh361f35'
          to='romeo@montague.lit/home'
          type='set'>
        <query xmlns='jabber:iq:roster' ver='ver96'>
          <item jid='juliet@shakespeare.lit'
                name='Juliet'
                subscription='both'>
            <group>VIPs</group>
          </item>
        </query>
      </iq>

   These "interim roster pushes" can be understood as follows:






Saint-Andre              Expires October 2, 2010               [Page 28]

Internet-Draft                   XMPP IM                      March 2010


   1.  Imagine that the client had an active presence session for the
       entire time between its cached roster version (say, "ver14") and
       the new roster version (say, "ver96").
   2.  During that time, the client might have received roster pushes
       related to various roster versions.  However, some of those
       roster pushes might have contained intermediate updates to the
       same roster item (e.g., modifications to the subscription state
       for bill@shakespeare.lit from "none" to "to" and from "to" to
       "both").
   3.  The interim roster pushes would not include all of the
       intermediate steps, only the final result of all modifications
       applied to each item while the client was in fact offline (say,
       "ver34", "ver42", "ver72", and "ver96").

   The client MUST handle an "interim roster push" in the same way it
   handles any roster push (indeed, from the client's perspective it
   cannot tell the difference between an "interim" roster push and a
   "live" roster push).  If the client's session ends before it receives
   all of the interim roster pushes, when requesting the roster after
   reconnection it SHOULD request the version associated with the last
   roster push it received during the session that was disconnected, not
   the version associated with the roster result it received at the
   start of the session that was disconnected.

   When roster versioning is enabled, the server MUST include the
   updated roster version with each roster push.  Roster pushes MUST
   occur in order of modification and the version contained in a roster
   push MUST be unique.  Even if the client has not included the 'ver'
   attribute in its roster gets or sets, the server SHOULD include the
   'ver' attribute on all roster pushes and results that it sends to the
   client.

      Note: Implementation guidelines and more detailed examples for
      roster versioning are provided in [XEP-0237].


3.  Managing Presence Subscriptions

   In order to protect the privacy of instant messaging users, presence
   information is disclosed only to other entities that a user has
   approved.  When a user has agreed that another entity is allowed to
   view its presence, the entity is said to have a SUBSCRIPTION to the
   user's presence.  An entity that has a subscription to a user's
   presence or to which a user has a presence subscription is called a
   CONTACT (in this document the term "contact" is also used in a less
   strict sense to refer to a potential contact or an item in a user's
   roster).




Saint-Andre              Expires October 2, 2010               [Page 29]

Internet-Draft                   XMPP IM                      March 2010


   In XMPP, a subscription lasts across presence sessions; indeed, it
   lasts until the contact unsubscribes or the user cancels the
   previously-granted subscription.

   Subscriptions are managed within XMPP by sending presence stanzas
   containing specially-defined attributes ("subscribe", "unsubscribe",
   "subscribed", and "unsubscribed").

      Note: When a server processes or generates an outbound presence
      stanza of type "subscribe", "subscribed", "unsubscribe", or
      "unsubscribed", the server MUST stamp the outgoing presence stanza
      with the bare JID <node@domain> of the sending entity, not the
      full JID <node@domain/resource>.  Enforcement of this rule
      simplifies the presence subscription model and helps to prevent
      presence leaks; for information about presence leaks, refer to the
      security considerations of [XMPP-CORE].

   Subscription states are reflected in the rosters of both the user and
   the contact.  Complete details regarding these subscription states
   can be found Appendix A; those details are not provided in this
   section, which simply narrates the protocol flows for common use
   cases related to presence subscriptions.

3.1.  Requesting a Subscription

   A SUBSCRIPTION REQUEST is a request from a user for authorization to
   permanently subscribe to a contact's presence information;
   syntactically it is a presence stanza whose 'type' attribute has a
   value of "subscribe".  A subscription request is generated by a
   user's client, processed by the (potential) contact's server, and
   acted on by the contact via the contact's client.  The workflow is
   described in the following sections.

      Note: Presence subscription requests are sent to available
      resources, whereas the roster pushes associated with subscription
      state changes are sent to interested resources.  Therefore if a
      resource wishes to receive both subscription requests and roster
      pushes, it MUST both send initial presence and request the roster.

3.1.1.  Client Generation of Outbound Subscription Request

   A user's client generates a subscription request by sending a
   presence stanza of type "subscribe" and specifying a 'to' address of
   the potential contact's bare JID <contact@domain>.

   UC: <presence id='xk3h1v69'
                 to='juliet@example.com'
                 type='subscribe'/>



Saint-Andre              Expires October 2, 2010               [Page 30]

Internet-Draft                   XMPP IM                      March 2010


   When a user sends a presence subscription request to a potential
   instant messaging and presence contact, the value of the 'to'
   attribute MUST be a bare JID <contact@domain> rather a full JID
   <contact@domain/resource>, since the desired result is for the user
   to receive presence from all of the contact's resources, not merely
   the particular resource specified in the 'to' attribute.  Use of bare
   JIDs also simplifies subscription processing, presence probes, and
   presence notifications by the user's server and the contact's server.

   For tracking purposes, a client SHOULD include an 'id' attribute in a
   presence subscription request.

      Note: Many XMPP clients prompt the user for information about the
      potential contact (e.g., "handle" and desired roster group) when
      generating an outbound presence subscription request and therefore
      send a roster set before sending the outbound presence
      subscription request.  This behavior is OPTIONAL, because a client
      MAY instead wait until receiving the initial roster push from the
      server before uploading user-provided information about the
      contact.  A server MUST process a roster set and outbound presence
      subscription request in either order.

3.1.2.  Server Processing of Outbound Subscription Request

   Upon receiving the outbound presence subscription request, the user's
   server MUST proceed as follows.

   1.  Before processing the request, the user's server SHOULD check the
       syntax of the JID contained in the 'to' attribute.  If the JID is
       of the form <contact@domain/resource> instead of
       <contact@domain>, the user's server SHOULD treat it as if the
       request had been directed to the contact's bare JID and modify
       the 'to' address accordingly.  The server MAY also verify that
       the JID adheres to the format defined in [XMPP-CORE], including
       checking against the relevant stringprep profiles.
   2.  If the potential contact is hosted on the same server as the
       user, then the server MUST adhere to the rules specified in the
       next section in processing the subscription request and
       delivering it to the (local) contact.
   3.  If the potential contact is hosted on a remote server, subject to
       local service policies the user's server MUST then route the
       stanza to that remote domain in accordance with core XMPP stanza
       processing rules.  (This can result in returning an appropriate
       stanza error to the user, such as <remote-server-timeout/>.)

   As mentioned, before locally delivering or remotely routing the
   presence subscription request, the user's server MUST stamp the
   outbound subscription request with the bare JID <user@domain> of the



Saint-Andre              Expires October 2, 2010               [Page 31]

Internet-Draft                   XMPP IM                      March 2010


   user.

   US: <presence from='romeo@example.net'
                 id='xk3h1v69'
                 to='juliet@example.com'
                 type='subscribe'/>

   If the presence subscription request cannot be locally delivered or
   remotely routed (e.g., because the request is malformed, the local
   contact does not exist, the remote server does not exist, an attempt
   to contact the remote server times out, or any other error determined
   or experienced by the user's server), then the user's server MUST
   return an appropriate error stanza to the user.  An example follows.

   US: <presence from='juliet@example.com'
                 id='xk3h1v69'
                 to='romeo@example.net'
                 type='error'>
         <error type='modify'>
           <remote-server-not-found
               xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
         </error>
       </presence>

   After locally delivering or remotely routing the presence
   subscription request, the user's server MUST then send a roster push
   to all of the user's interested resources, containing the potential
   contact with a subscription state of "none" and with notation that
   the subscription is pending (via an 'ask' attribute whose value is
   "subscribe").





















Saint-Andre              Expires October 2, 2010               [Page 32]

Internet-Draft                   XMPP IM                      March 2010


   US: <iq id='b89c5r7ib574'
           to='romeo@example.net/foo'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item ask='subscribe'
                 jid='juliet@example.com'
                 subscription='none'/>
         </query>
       </iq>

   US: <iq id='b89c5r7ib575'
           to='romeo@example.net/bar'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item ask='subscribe'
                 jid='juliet@example.com'
                 subscription='none'/>
           </item>
         </query>
       </iq>

   If the contact does not approve or deny the subscription request
   within some configurable amount of time, the user's server SHOULD
   resend the subscription request to the contact based on an
   implementation-specific algorithm (e.g., whenever a new resource
   becomes available for the user, or after a certain amount of time has
   elapsed); this helps to recover from transient, silent errors that
   might have occurred in relation to the original subscription request.

3.1.3.  Server Processing of Inbound Subscription Request

   Before processing the inbound presence subscription request, the
   contact's server SHOULD check the syntax of the JID contained in the
   'to' attribute.  If the JID is of the form <contact@domain/resource>
   instead of <contact@domain>, the contact's server SHOULD treat it as
   if the request had been directed to the contact's bare JID and modify
   the 'to' address accordingly.  The server MAY also verify that the
   JID adheres to the format defined in [XMPP-CORE], including checking
   against the relevant stringprep profiles.

   When processing the inbound presence subscription request, the
   contact's server MUST adhere to the following rules:

   1.  Above all, the contact's server MUST NOT automatically approve
       subscription requests on the contact's behalf (unless the contact
       has configured its account to automatically approve subscription
       requests or has accepted an agreement with its service provider
       that allows such behavior, for instance via an employment



Saint-Andre              Expires October 2, 2010               [Page 33]

Internet-Draft                   XMPP IM                      March 2010


       agreement within an enterprise deployment).  Instead, if a
       subscription request requires approval then the contact's server
       MUST deliver that request to the contact's available resource(s)
       for approval or denial by the contact.
   2.  If the contact does not exist, then the contact's server MUST
       automatically return a presence stanza of type "unsubscribed" to
       the user.

   CS: <presence from='juliet@example.com'
                 id='xk3h1v69'
                 to='romeo@example.net'
                 type='unsubscribed'/>

   3.  If the contact exists and the user already has a subscription to
       the contact's presence, then the contact's server MUST auto-reply
       on behalf of the contact by sending a presence stanza of type
       "subscribed" from the contact's bare JID to the user's bare JID.
       If the contact previously sent a presence stanza of type
       "subscribed" and the contact's server treated that as indicating
       "pre-approval" for the user's presence subscription (see
       Appendix A), then the contact's server SHOULD also auto-reply on
       behalf of the contact.

   CS: <presence from='juliet@example.com'
                 id='xk3h1v69'
                 to='romeo@example.net'
                 type='subscribed'/>

   4.  If the contact exists, the user does not already have a
       subscription to the contact's presence, and there is at least one
       available resource associated with the contact when the
       subscription request is received by the contact's server, then
       the contact's server MUST broadcast that subscription request to
       all available resources in accordance with Section 8.  As a way
       of acknowledging receipt of the presence subscription request,
       the contact's server MAY send a presence stanza of type
       "unavailable" from the bare JID of the contact to the bare JID of
       the user (the user's client MUST NOT assume that this ack
       provides presence information about the contact, since it comes
       from the contact's bare JID and is received before the
       subscription request has been approved).
   5.  If the contact exists, the user does not already have a
       subscription to the contact's presence, and the contact has no
       available resources when the subscription request is received by
       the contact's server, then the contact's server MUST keep a
       record of the complete presence stanza comprising the
       subscription request, including any extended content contained
       therein, and deliver the request when the contact next has an



Saint-Andre              Expires October 2, 2010               [Page 34]

Internet-Draft                   XMPP IM                      March 2010


       available resource.  The contact's server MUST continue to
       deliver the subscription request whenever the contact creates an
       available resource, until the contact either approves or denies
       the request.  (The contact's server MUST NOT deliver more than
       one subscription request from any given user when the contact
       next has an available resource; e.g., if the user sends multiple
       subscription requests to the contact while the contact is
       offline, the contact's server SHOULD store only one of those
       requests, such as the first request or last request, and MUST
       deliver only one of the requests when the contact next has an
       available resource; this helps to prevent "subscription request
       spam".)  As a way of acknowledging receipt of the presence
       subscription request, the contact's server MAY send a presence
       stanza of type "unavailable" from the bare JID of the contact to
       the bare JID of the user, since it comes from the contact's bare
       JID and is received before the subscription request has been
       approved).

      Note: Until and unless the contact approves the subscription
      request as described under Section 3.1.4, the contact's server
      MUST NOT add an item for the user to the contact's roster.

3.1.4.  Client Processing of Inbound Subscription Request

   When the contact's client receives a subscription request from the
   user, it MUST present the request to the contact for approval (unless
   the contact has explicitly configured the client to automatically
   approve or deny some or all subscription requests).

   A subscription request is approved by sending a presence stanza of
   type "subscribed", which is processed as described in the following
   sections for both the contact's server and the user's server.

   CC: <presence to='romeo@example.net' type='subscribed'/>

   A subscription request is denied by sending a presence stanza of type
   "unsubscribed", which is processed as described under Section 3.2 for
   both the contact's server and the user's server.

   CC: <presence to='romeo@example.net' type='unsubscribed'/>

3.1.5.  Server Processing of Outbound Subscription Approval

   When the contact's client sends the subscription approval, the
   contact's server MUST stamp the outbound stanza with the bare JID
   <contact@domain> of the contact and locally deliver or remotely route
   the stanza to the user.




Saint-Andre              Expires October 2, 2010               [Page 35]

Internet-Draft                   XMPP IM                      March 2010


   CS: <presence from='juliet@example.com'
                 to='romeo@example.net'
                 type='subscribed'/>

   The contact's server then MUST send a roster push to all of the
   contact's interested resources.

   CS: <iq id='a78b4q6ha463'
           to='juliet@example.com/balcony'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='from'/>
         </query>
       </iq>

   CS: <iq id='a78b4q6ha464'
           to='juliet@example.com/chamber'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='from'/>
         </query>
       </iq>

   The contact's server MUST then also send current presence to the user
   from each of the contact's available resources.

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   CS: <presence from='juliet@example.com/chamber'
                 to='romeo@example.net'/>

   From the perspective of the contact, there now exists a subscription
   from the user.

   In order to subscribe to the user's presence, the contact would then
   send a subscription request to the user.  (XMPP clients will often
   automatically send the subscription request instead of requiring the
   contact to initiate the subscription request, since it is assumed
   that the desired end state is a mutual subscription.)  Naturally,
   when the contact sends a subscription request to the user, the
   subscription states will be different from those shown in the
   foregoing examples (see Appendix A) and the roles will be reversed.






Saint-Andre              Expires October 2, 2010               [Page 36]

Internet-Draft                   XMPP IM                      March 2010


3.1.6.  Server Processing of Inbound Subscription Approval

   When the user's server receives the subscription approval, it MUST
   first check if the contact is in the user's roster with
   subscription='none' or subscription='from' and the 'ask' flag set to
   "subscribe" (i.e., a subscription state of "None + Pending Out",
   "None + Pending Out+In", or "From + Pending Out"; see Appendix A).
   If this check is successful, the user's server MUST:

   1.  Deliver the inbound subscription approval to all of the user's
       interested resources (this helps to give the user's client(s)
       proper context regarding the subscription approval so that they
       can differentiate between a roster push originated by another of
       the user's resources and a subscription approval received from
       the contact).  This MUST occur before sending the roster push
       described in the next step.

   US: <presence from='juliet@example.com'
                 to='romeo@example.net'
                 type='subscribed'/>

   2.  Initiate a roster push to all of the user's interested resources,
       containing an updated roster item for the contact with the
       'subscription' attribute set to a value of "to" (if the
       subscription state was "None + Pending Out" or "None + Pending
       Out+In") or "both" (if the subscription state was "From + Pending
       Out").

   US: <iq id='b89c5r7ib576'
           to='romeo@example.net/foo'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='to'/>
         </query>
       </iq>

   US: <iq id='b89c5r7ib577'
           to='romeo@example.net/bar'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='to'/>
           </item>
         </query>
       </iq>





Saint-Andre              Expires October 2, 2010               [Page 37]

Internet-Draft                   XMPP IM                      March 2010


   3.  The user's server MUST also deliver the available presence stanza
       received from each of the contact's available resources to each
       of the user's available resources.

   [ ... to resource1 ... ]

   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   [ ... to resource2 ... ]

   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   [ ... to resource1 ... ]

   US: <presence from='juliet@example.com/chamber'
                 to='romeo@example.net'/>

   [ ... to resource2 ... ]

   US: <presence from='juliet@example.com/chamber'
                 to='romeo@example.net'/>

   Otherwise -- that is, if the user does not exist, if the contact is
   not in the user's roster, or if the contact is in the user's roster
   with a subscription state other than those described in the foregoing
   check -- then the user's server MUST silently ignore the stanza by
   not delivering it to the user, not modifying the user's roster, and
   not generating a roster push to the user's interested resources.

   From the perspective of the user, there now exists a subscription to
   the contact's presence.

3.2.  Cancelling a Subscription

3.2.1.  Client Generation of Subscription Cancellation

   If a contact would like to cancel a subscription that it has
   previously granted to a user (or deny a subscription request), it
   sends a presence stanza of type "unsubscribed".

   CC: <presence to='romeo@example.net' type='unsubscribed'/>








Saint-Andre              Expires October 2, 2010               [Page 38]

Internet-Draft                   XMPP IM                      March 2010


3.2.2.  Server Processing of Outbound Subscription Cancellation

   Upon receiving the outound subscription cancellation, the contact's
   server MUST proceed as follows.

   1.  If the user is hosted on the same server as the contact, then the
       server MUST adhere to the rules specified in the next section in
       processing the subscription cancellation.
   2.  If the user is hosted on a remote server, subject to local
       service policies the contact's server MUST then route the stanza
       to that remote domain in accordance with core XMPP stanza
       processing rules.  (This can result in returning an appropriate
       stanza error to the contact, such as <remote-server-timeout/>.)

   As mentioned, before locally delivering or remotely routing the
   stanza, the contact's server MUST stamp the outbound subscription
   cancellation with the bare JID <contact@domain> of the contact.

   CS: <presence from='juliet@example.com'
                 to='romeo@example.net'
                 type='unsubscribed'/>

   The contact's server then MUST send a roster push with the updated
   roster item to all of the contact's interested resources, where the
   subscription state is now either "none" or "to" (see Appendix A).

   CS: <iq id='a78b4q6ha465'
           to='juliet@example.com/balcony'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='none'/>
         </query>
       </iq>

   CS: <iq id='a78b4q6ha466'
           to='juliet@example.com/chamber'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='none'/>
         </query>
       </iq>








Saint-Andre              Expires October 2, 2010               [Page 39]

Internet-Draft                   XMPP IM                      March 2010


3.2.3.  Server Processing of Inbound Subscription Cancellation

   When the user's server receives the inbound subscription
   cancellation, it MUST first check if the contact is in the user's
   roster with subscription='to' or subscription='both' (see
   Appendix A).  If this check is successful, the user's server MUST:

   1.  Deliver the inbound subscription cancellation to all of the
       user's interested resources (this helps to give the user's
       client(s) proper context regarding the subscription cancellation
       so that they can differentiate between a roster push originated
       by another of the user's resources and a subscription
       cancellation received from the contact).  This MUST occur before
       sending the roster push described in the next step.

   US: <presence from='juliet@example.com'
                 to='romeo@example.net'
                 type='unsubscribed'/>

   2.  Initiate a roster push to all of the user's interested resources,
       containing an updated roster item for the contact with the
       'subscription' attribute set to a value of "none" (if the
       subscription state was "To" or "To + Pending In") or "from" (if
       the subscription state was "Both").

   US: <iq id='h37h3u1bv400'
           to='romeo@example.net/foo'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='none'/>
         </query>
       </iq>

   US: <iq id='h37h3u1bv401'
           to='romeo@example.net/bar'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='none'/>
           </item>
         </query>
       </iq>

   Otherwise -- that is, if the user does not exist, if the contact is
   not in the user's roster, or if the contact is in the user's roster
   with a subscription state other than those described in the foregoing
   check -- then the user's server MUST silently ignore the stanza by



Saint-Andre              Expires October 2, 2010               [Page 40]

Internet-Draft                   XMPP IM                      March 2010


   not delivering it to the user, not modifying the user's roster, and
   not generating a roster push to the user's interested resources.

3.3.  Unsubscribing

3.3.1.  Client Generation of Unsubscribe

   If a user would like to unsubscribe from a contact's presence, it
   sends a presence stanza of type "unsubscribe".

   UC: <presence to='juliet@example.com' type='unsubscribe'/>

3.3.2.  Server Processing of Outbound Unsubscribe

   Upon receiving the outbound unsubscribe, the user's server MUST
   proceed as follows.

   1.  If the contact is hosted on the same server as the user, then the
       server MUST adhere to the rules specified in the next section in
       processing the subscription request.
   2.  If the contact is hosted on a remote server, subject to local
       service policies the user's server MUST then route the stanza to
       that remote domain in accordance with core XMPP stanza processing
       rules.  (This can result in returning an appropriate stanza error
       to the user, such as <remote-server-timeout/>.)

   As mentioned, before locally delivering or remotely routing the
   unsubscrbe, the user's server MUST stamp the stanza with the bare JID
   <user@domain> of the user.

   US: <presence from='romeo@example.net'
                 to='juliet@example.com'
                 type='unsubscribe'/>

   The user's server then MUST send a roster push with the updated
   roster item to all of the user's interested resources, where the
   subscription state is now either "none" or "from" (see Appendix A).














Saint-Andre              Expires October 2, 2010               [Page 41]

Internet-Draft                   XMPP IM                      March 2010


   US: <iq id='h37h3u1bv402'
           to='romeo@example.net/foo'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='none'/>
         </query>
       </iq>

   US: <iq to='romeo@example.net/bar'
           type='set'
           id='h37h3u1bv403'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='none'/>
           </item>
         </query>
       </iq>

3.3.3.  Server Processing of Inbound Unsubscribe

   When the contact's server receives the unsubscribe notification, it
   MUST first check if the user is in the contact's roster with
   subscription='from' or subscription='both' (i.e., a subscription
   state of "From", "From + Pending Out", or "Both"; see Appendix A).
   If this check is successful, the contact's server MUST:

   1.  Deliver the inbound unsubscribe to all of the contact's
       interested resources (this helps to give the contact's client(s)
       proper context regarding the unsubscribe so that they can
       differentiate between a roster push originated by another of the
       contact's resources and an unsubscribe received from the user).
       This MUST occur before sending the roster push described in the
       next step.

   CS: <presence from='romeo@example.net'
                 to='juliet@example.com'
                 type='unsubscribe'/>

   2.  Initiate a roster push to all of the contact's interested
       resources, containing an updated roster item for the contact with
       the 'subscription' attribute set to a value of "none" (if the
       subscription state was "From" or "From + Pending Out") or "to"
       (if the subscription state was "Both").







Saint-Andre              Expires October 2, 2010               [Page 42]

Internet-Draft                   XMPP IM                      March 2010


   CS: <iq id='a78b4q6ha467'
           to='juliet@example.com/balcony'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='none'/>
         </query>
       </iq>

   CS: <iq id='a78b4q6ha468'
           to='juliet@example.com/chamber'
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='none'/>
         </query>
       </iq>

   3.  Deliver the inbound unavailable notification to all of the
       contact's interested resources.

   CS: <presence from='romeo@example.net'
                 to='juliet@example.com'
                 type='unavailable'/>

   Note: The user's client MUST NOT depend on receiving the unsubscribe
   and the unavailable presence notification, since it MUST consider its
   presence subscription to the contact, and its presence information
   about the contact, to be null and void when it sends the presence
   stanza of type "unusbscribe" or when receives the roster push
   triggered by the unsubscribe request.

   Otherwise -- that is, if the contact does not exist, if the user is
   not in the contact's roster, or if the user is in the contact's
   roster with a subscription state other than those described in the
   foregoing check -- then the contact's server MUST silently ignore the
   stanza by not delivering it to the contact, not modifying the
   contact's roster, and not generating a roster push to the contact's
   interested resources.  However, if the contact's server is keeping
   track of an inbound presence subscription request from the user to
   the contact but the user is not in the contact's roster (functionally
   equivalent to a subscription state of "None + Pending In" where the
   contact never added the user to the contact's roster), then the
   contact's server MUST simply remove any record of the inbound
   presence subscription request (it cannot remove the user from the
   contact's roster because the user was never added to the contact's
   roster).




Saint-Andre              Expires October 2, 2010               [Page 43]

Internet-Draft                   XMPP IM                      March 2010


4.  Exchanging Presence Information

4.1.  Overview

   The concept of presence refers to an entity's availability for
   communication over a network.  At the most basic level, presence is a
   boolean "on/off" variable that signals whether an entity is available
   or unavailable for communication (the terms "online" and "offline"
   are also used).  In XMPP, a user's availability is signalled when a
   client controlled by the user generates a <presence/> stanza with no
   'type' attribute, and an entity's lack of availability is signalled
   when a client generates a <presence/> stanza whose 'type' attribute
   has a value of "unavailable".

   XMPP presence typically follows a "publish-subscribe" or "observer"
   pattern, wherein an entity sends presence to its server, and its
   server then broadcasts that information to all of the entity's
   contacts who have a subscription to the entity's presence (in the
   terminology of [IMP-MODEL], an entity that generates presence is a
   "presentity" and the entities that receive presence are
   "subscribers").  A client generates presence for broadcasting to all
   subscribed entities by sending a presence stanza to its server with
   no 'to' address, where the presence stanza has either no 'type'
   attribute or a 'type' attribute whose value is "unavailable".  This
   kind of presence is called BROADCAST PRESENCE.  (A client can also
   send DIRECTED PRESENCE, i.e., a presence stanza with a 'to' address;
   this is less common but is sometimes used to send presence to
   entities that are not subscribed to the user's presence; see
   Section 4.6.)

   After a client completes the preconditions specified in [XMPP-CORE],
   it can establish a PRESENCE SESSION at its server by sending initial
   presence (Section 4.2), where the presence session is terminated by
   sending unavailable presence (Section 4.5).  For the duration of its
   presence session, a connected resource (in the terminology of
   [XMPP-CORE]) is said to be an AVAILABLE RESOURCE.

   In XMPP-based applications that combine messaging and presence
   functionality, the default type of communication for which presence
   signals availability is messaging; however, it is not necessary for
   XMPP-based applications to combine messaging and presence
   functionality, and can provide standalone presence features without
   messaging (in addition, XMPP servers do not require information about
   network availability in order to successfully route message and IQ
   stanzas).






Saint-Andre              Expires October 2, 2010               [Page 44]

Internet-Draft                   XMPP IM                      March 2010


      Note: In the following examples, the "user" is juliet@example.com
      and the user has three contacts in her roster with a subscription
      state of "from" or "both": romeo@example.net,
      mercutio@example.com, and benvolio@example.net.

4.2.  Initial Presence

4.2.1.  Client Generation of Initial Presence

   After completing the preconditions described in [XMPP-CORE]
   (REQUIRED) and requesting the roster (RECOMMENDED), a client signals
   its availability for communication by sending INITIAL PRESENCE to its
   server, i.e., a presence stanza with no 'to' address (indicating that
   it is meant to be broadcast by the server on behalf of the client)
   and no 'type' attribute (indicating the user's availability).

   UC: <presence/>

   The initial presence stanza MAY contain the <priority/> element, the
   <show/> element, and one or more instances of the <status/> element,
   as well as extended content.

4.2.2.  Server Processing of Outbound Presence

   Upon receiving initial presence from a client, the user's server MUST
   send the initial presence stanza from the full JID
   <user@domain/resource> of the user to all contacts that are
   subscribed to the user's presence; such contacts are those for which
   a JID is present in the user's roster with the 'subscription'
   attribute set to a value of "from" or "both".

   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   US: <presence from='juliet@example.com/balcony'
                 to='mercutio@example.com'/>

   US: <presence from='juliet@example.com/balcony'
                 to='benvolio@example.net'/>

   The user's server MUST also broadcast initial presence from the
   user's newly available resource to all of the user's available
   resources (including the resource that generated the presence
   notification in the first place).







Saint-Andre              Expires October 2, 2010               [Page 45]

Internet-Draft                   XMPP IM                      March 2010


   US: <presence from='juliet@example.com/balcony'
                 to='juliet@example.com/balcony'/>

   US: <presence from='juliet@example.com/balcony'
                 to='juliet@example.com/chamber'/>

   In the absence of presence information about the user's contacts, the
   user's server MUST also send presence probes to the user's contacts
   on behalf of the user as specified under Section 4.3.

4.2.3.  Server Processing of Inbound Presence

   Upon receiving presence from the user, the contact's server MUST
   deliver the user's presence stanza to all of the contact's available
   resources.

   [ ... to resource1 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   [ ... to resource2 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   If there is no such contact, the contact's server MUST silently
   ignore the presence stanza.

4.2.4.  Client Processing of Inbound Presence

   When the contact's client receives presence from the user, it SHOULD
   proceed as follows:

   1.  If the user is in the contact's roster, the client MUST display
       the presence information in an appropriate roster interface.
   2.  If the user is not in the contact's roster but the contact and
       the user are actively exchanging message or IQ stanzas, the
       contact's client SHOULD display the presence information in the
       user interface for that chat session (see also Section 4.6 and
       Section 5.1).
   3.  Otherwise, the client MUST ignore the presence information and
       not display it to the contact.

4.3.  Presence Probes

   A PRESENCE PROBE is a request for a contact's current presence
   information, sent on behalf of a user by the user's server;



Saint-Andre              Expires October 2, 2010               [Page 46]

Internet-Draft                   XMPP IM                      March 2010


   syntactically it is a presence stanza whose 'type' attribute has a
   value of "probe".  In the context of presence subscriptions, the
   value of the 'from' address MUST be the bare or full JID of the
   subscribed user and the value of the 'to' address SHOULD be the bare
   JID of the contact to which the user is subscribed (since presence
   subscriptions are based on the bare JID) but MAY be a full JID for
   the contact.  (Probes can also be sent outside the context of a
   presence subscription, e.g. when the contact has sent directed
   presence to an entity as described under Section 4.6.)

   US: <presence from='juliet@example.com/balcony'
                 id='ign291v5'
                 to='romeo@example.net'
                 type='probe'/>

      Note: Although presence probes MAY be sent by a client, in general
      a client will not need to send them since the task of gathering
      presence from a user's contacts is managed by the user's server.
      However, if a client generates an outbound presence probe then the
      user's server SHOULD route the probe (if the contact is at another
      server) or process the probe (if the contact is at the same
      server) and MUST NOT return a stanza or stream error to the
      client.

4.3.1.  Server Generation of Outbound Presence Probe

   When a server needs to discover the availability of a user's contact,
   it sends a presence probe from the full JID <user@domain/resource> of
   the user to the bare JID <contact@domain> of the contact.  The server
   MUST NOT send a probe to a contact if the user is not subscribed to
   the contact's presence (i.e., if the contact is not in the user's
   roster with the 'subscription' attribute set to a value of "to" or
   "both".

   The user's server SHOULD send a presence probe whenever the user
   starts a new presence session by sending initial presence; however,
   the server MAY choose not to send the probe at that point if it has
   what it deems to be reliable and up-to-date presence information
   about the user's contacts (e.g., because the user has another
   available resource or because the user briefly logged off and on
   before the new presence session began).  In addition, a server MAY
   periodically send a presence probe to a contact if it has not
   received presence information or other traffic from the contact in
   some configurable amount of time; this can help to prevent "ghost"
   contacts who appear to be online but in fact are not.






Saint-Andre              Expires October 2, 2010               [Page 47]

Internet-Draft                   XMPP IM                      March 2010


   US: <presence from='juliet@example.com/balcony'
                 id='ign291v5'
                 to='romeo@example.net'
                 type='probe'/>

   US: <presence from='juliet@example.com/balcony'
                 id='xv291f38'
                 to='mercutio@example.com'
                 type='probe'/>

   Naturally, the user's server does not need to send a presence probe
   to a contact if the contact's account resides on the same server as
   the user, since the server possesses contact's information locally.

4.3.2.  Server Processing of Inbound Presence Probe

   Upon receiving a presence probe to the contact's bare JID from the
   user's server on behalf of the user, the contact's server SHOULD
   reply as follows:

   1.  If the contact account does not exist or the user is in the
       contact's roster with a subscription state other than "From",
       "From + Pending Out", or "Both" (as defined under Appendix A) and
       the contact has not sent directed presence to the user (as
       defined under Section 4.6), then the contact's server MUST return
       a presence stanza of type "unsubscribed" in response to the
       presence probe (however, if a server receives a presence probe
       from a configured hostname of the server itself or another such
       trusted service, it MAY provide presence information about the
       user to that entity).

   CS: <presence from='mercutio@example.com'
                 id='xv291f38'
                 to='juliet@example.com'
                 type='unsubscribed'/>

   2.  Else, if the contact has moved temporarily or permanently to
       another address, then the server SHOULD return a presence stanza
       of type "error" with a stanza error condition of <redirect/>
       (temporary) or <gone/> (permanent) that includes the new address
       of the contact.










Saint-Andre              Expires October 2, 2010               [Page 48]

Internet-Draft                   XMPP IM                      March 2010


   CS: <presence from='mercutio@example.com'
                 id='xv291f38'
                 to='juliet@example.com'
                 type='error'>
         <error type='modify'>
           <gone xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
             xmpp:la-mer@example.com
           </gone>
         </error>
       </presence>

   3.  Else, if the contact has no available resources, then the server
       SHOULD reply to the presence probe by sending to the user a
       presence stanza of type "unavailable" (although sending
       unavailable presence here is preferable because it results in a
       deterministic answer to the probe, it is not mandatory because it
       can greatly increase the number of presence notifications
       generated by the contact's server); if appropriate in accordance
       with local security policies this presence notification MAY
       include the full XML of the last unavailable presence stanza that
       the server received from the contact (including the 'id' of the
       original stanza), but if not then the presence notification
       SHOULD simply indicate that the contact is unavailable without
       any of the details originally provided; in any case the presence
       notification returned to the probing entity SHOULD include
       information about the time when the last unavailable presence
       stanza was generated (formatted using the XMPP delayed delivery
       extension [DELAY]).

   CS: <presence from='mercutio@example.com'
                 id='xv291f38'
                 to='juliet@example.com'
                 type='unavailable'>
         <delay xmlns='urn:xmpp:delay'
                stamp='2002-09-10T23:41:07Z'/>
       </presence>

   4.  Else, if the contact has at least one available resource, then
       the server MUST reply to the presence probe by sending to the
       user the full XML of the last presence stanza with no 'to'
       attribute received by the server from each of the contact's
       available resources.









Saint-Andre              Expires October 2, 2010               [Page 49]

Internet-Draft                   XMPP IM                      March 2010


   CS: <presence from='romeo@example.net/foo'
                 id='hzf1v27k'
                 to='juliet@example.com'/>

   CS: <presence from='romeo@example.net/bar'
                 id='ps6t1fu3'
                 to='juliet@example.com'>
         <show>away</show>
       </presence>

   If the contact's server receives a presence probe addressed to a full
   JID of the contact, the server MUST NOT return presence information
   about any resource except the resource specified by the 'to' address
   of the probe.  Rules #1 and #2 for a bare JID probe apply equally to
   the case of a full JID probe.  If there is a resource matching the
   full JID and (a) the probing entity has authorization via a presence
   subscription to see the contact's presence or (b) the contact has
   sent directed available presence to the probing entity, then the
   server MUST return an available presence notification, which SHOULD
   communicate only the fact that the resource is available (not
   detailed information such as the <show/>, <status/>, <priority/>, or
   presence extensions).


   CS: <presence from='romeo@example.net/bar'
                 to='lobby@chat.example.com'/>

      Note: The handling of the 'id' attribute in relation to presence
      probes was unspecified in the predecessor to this specification.
      Although the pattern of "send a probe and receive a reply" might
      seem like a request-response protocol, in fact it is not because
      the response to a probe might consist of multiple presence stanzas
      (one for each available resource currently active for the
      contact).  For this reason, if the contact currently has available
      resources then the contact's server SHOULD preserve the 'id'
      attribute of the contact's original presence stanza (if any) when
      sending those presence notifications to the probing entity;
      however, if the contact currently has no available resources, the
      probing entity is not authorized (via presence subscription) to
      see the contact's presence, or an error occurs in relation to the
      proble, then the contact's server SHOULD mirror the 'id' of the
      presence probe when replying to the probing entity.

4.4.  Subsequent Presence Broadcast







Saint-Andre              Expires October 2, 2010               [Page 50]

Internet-Draft                   XMPP IM                      March 2010


4.4.1.  Client Generation of Presence Broadcast

   After sending initial presence, the user's client can update its
   availability for broadcasting at any time during its session by
   sending a presence stanza with no 'to' address and no 'type'
   attribute.

   UC: <presence>
         <show>away</show>
       </presence>

   The presence broadcast MAY contain the <priority/> element, the
   <show/> element, and one or more instances of the <status/> element,
   as well as extended content.

   However, a user SHOULD send a presence update only to broadcast
   information that is relevant to the user's availability for
   communication or the communication capabilities of the connected
   resource.  Information that is not relevant in this way can be of
   interest to the user's contacts but SHOULD be sent via other means,
   such as the XMPP message stanza.

4.4.2.  Server Processing of Outbound Presence

   Upon receiving a presence stanza expressing updated availability, the
   user's server MUST broadcast the full XML of that presence stanza to
   the contacts who meet all of the following criteria:

   1.  The contact is in the user's roster with a subscription type of
       "from" or "both".
   2.  The last presence stanza received from the contact during the
       user's presence session was not of type "error" or "unsubscribe".

   As an optimization, if the subscription type is "both", then the
   server SHOULD send subsequent presence notifications to a contact
   only if the contact is online according to the user's server.  That
   is, if the user's server never received a positive indication that
   the contact is online in response to the presence probe it sent to
   the contact or if the last presence stanza it received from the
   contact during the user's presence session was of type "unavailable",
   the user's server SHOULD NOT send subsequent presence notifications
   from the user to the contact.  This optimization helps to save
   bandwidth, since most presence subscriptions are bidirectional and
   many contacts will not be online at any given time.







Saint-Andre              Expires October 2, 2010               [Page 51]

Internet-Draft                   XMPP IM                      March 2010


   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'>
         <show>away</show>
       </presence>

   US: <presence from='juliet@example.com/balcony'
                 to='benvolio@example.net'>
         <show>away</show>
       </presence>

   US: <presence from='juliet@example.com/balcony'
                 to='mercutio@example.com'>
         <show>away</show>
       </presence>

      See Section 4.6 regarding rules that supplement the foregoing for
      handling of directed presence.

   The user's server MUST also send the presence stanza to all of the
   user's available resources (including the resource that generated the
   presence notification in the first place).

   US: <presence from='juliet@example.com/balcony'
                 to='juliet@example.com/chamber'>
         <show>away</show>
       </presence>

   US: <presence from='juliet@example.com/balcony'
                 to='juliet@example.com/balcony'>
         <show>away</show>
       </presence>

4.4.3.  Server Processing of Inbound Presence

   Upon receiving presence from the user, the contact's server MUST
   deliver the user's presence stanza to all of the contact's available
   resources.














Saint-Andre              Expires October 2, 2010               [Page 52]

Internet-Draft                   XMPP IM                      March 2010


   [ ... to resource1 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'>
         <show>away</show>
       </presence>

   [ ... to resource2 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'>
         <show>away</show>
       </presence>

4.4.4.  Client Processing of Inbound Presence

   When the contact's client receives presence from the user, it SHOULD
   proceed as follows:

   1.  If the user is in the contact's roster, the client MUST display
       the presence information in an appropriate roster interface.
   2.  If the user is not in the contact's roster but the contact and
       the user are actively exchanging message or IQ stanzas, the
       contact's client SHOULD display the presence information in the
       user interface for that chat session (see also Section 4.6 and
       Section 5.1).
   3.  Otherwise, the client MUST ignore the presence information and
       not display it to the contact.

4.5.  Unavailable Presence

4.5.1.  Client Generation of Unavailable Presence

   Before ending its presence session with a server, the user's client
   SHOULD gracefully become unavailable by sending UNAVAILABLE PRESENCE,
   i.e., a presence stanza that possesses no 'to' attribute and that
   possesses a 'type' attribute whose value is "unavailable".

   UC: <presence type='unavailable'/>

   Optionally, the unavailable presence stanza MAY contain one or more
   <status/> elements specifying the reason why the user is no longer
   available.

   UC: <presence type='unavailable'>
         <status>going on vacation</status>
       </presence>




Saint-Andre              Expires October 2, 2010               [Page 53]

Internet-Draft                   XMPP IM                      March 2010


   However, the unavailable presence stanza MUST NOT contain the
   <priority/> element or the <show/> element, since these elements
   apply only to available presence.

4.5.2.  Server Processing of Outbound Unavailable Presence

   The user's server MUST NOT depend on receiving unavailable presence
   from an available resource, since the resource can become unavailable
   ungracefully (e.g., the resource can be timed out by the server
   because of inactivity).

   If an available resource becomes unavailable for any reason (either
   gracefully or ungracefully), the user's server MUST broadcast
   unavailable presence to all contacts that meet all of the following
   criteria:

   1.  The contact is in the user's roster with a subscription type of
       "from" or "both".
   2.  The last presence stanza received from the contact during the
       user's presence session was not of type "error" or "unsubscribe".

      See Section 4.6 regarding rules that supplement the foregoing for
      handling of directed presence.

      The optimization employed for subsequent presence broadcast during
      a user's presence session MUST NOT be employed for unavailable
      presence broadcast; if it were, the last presence received by the
      contact's server would be the user's initial presence for the
      presence session, with the result that the contact would consider
      the user to be online.

   If the unavailable notification was gracefully received from the
   client, then the server MUST broadcast the full XML of the presence
   stanza.

















Saint-Andre              Expires October 2, 2010               [Page 54]

Internet-Draft                   XMPP IM                      March 2010


   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'
                 type='unavailable'/>
         <status>going on vacation</status>
       </presence>

   US: <presence from='juliet@example.com/balcony'
                 to='benvolio@example.net'
                 type='unavailable'>
         <status>going on vacation</status>
       </presence>

   US: <presence from='juliet@example.com/balcony'
                 to='mercutio@example.com'
                 type='unavailable'>
         <status>going on vacation</status>
       </presence>

   The user's server MUST also send the unavailable notification to all
   of the user's available resources (including the resource that
   generated the presence notification in the first place).

   US: <presence from='juliet@example.com/balcony'
                 to='juliet@example.com/chamber'
                 type='unavailable'>
         <status>going on vacation</status>
       </presence>

   If the server detects that the user has gone offline ungracefully,
   then the server MUST generate the unavailable presence broadcast on
   the user's behalf.

      Note: Any presence stanza with no 'type' attribute and no 'to'
      attribute that is sent after sending unavailable presence
      broadcast MUST be sent by the user's server to all subscribers
      (i.e., MUST be treated as equivalent to initial presence for a new
      presence session).

4.5.3.  Server Processing of Inbound Unavailable Presence

   Upon receiving an unavailable notification from the user, the
   contact's server MUST deliver the user's presence stanza to all of
   the contact's available resources.








Saint-Andre              Expires October 2, 2010               [Page 55]

Internet-Draft                   XMPP IM                      March 2010


   [ ... to resource1 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'
                 type='unavailable'>
         <status>going on vacation</status>
       </presence>

   [ ... to resource2 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'
                 type='unavailable'>
         <status>going on vacation</status>
       </presence>

   If the contact's server is optimizing subsequent presence delivery as
   described under Section 4.4, it MUST also note that the user is
   unavailable and appropriately update its internal representation of
   which entities are online.

4.5.4.  Client Processing of Inbound Unavailable Presence

   When the contact's client receives an unavailable notification from
   the user, it SHOULD proceed as follows:

   1.  If the user is in the contact's roster, the client MUST display
       the unavailable notification in an appropriate roster interface.
   2.  If the user is not in the contact's roster but the contact and
       the user are actively exchanging message or IQ stanzas, the
       contact's client SHOULD display the unavailable notification in
       the user interface for that chat session (see also Section 4.6
       and Section 5.1).
   3.  Otherwise, the client MUST ignore the unavailable notification
       and not display it to the contact.

   Typically, presence is presence about a particular connected
   resource.  However, it is possible for the contact to receive an
   unavailable notification from the bare JID of the user.  In this
   case, the presence notificatio SHOULD be treated as related to a
   resource identifier of zero length, which does not supersede or
   overshadow other resources associated with the same bare JID.

4.6.  Directed Presence

   This section supplements and in some respects modifies the rules for
   client and server processing of presence notifications, but only for
   the special case of directed presence.



Saint-Andre              Expires October 2, 2010               [Page 56]

Internet-Draft                   XMPP IM                      March 2010


4.6.1.  Client Generation of Directed Presence

   As noted, directed presence is a presence stanza with a 'to'
   attribute whose value is the bare JID or full JID of the other entity
   and with either no 'type' attribute (indicating availability) or a
   'type' attribute whose value is "unavailable".

   Information about the use of directed presence in the context of a
   one-to-one chat session is provided under Section 5.1.

4.6.2.  Server Processing of Outbound Directed Presence

   When the user's server receives a directed presence stanza, it SHOULD
   process it according to the following rules.

   1.  If the user sends directed available or unavailable presence to a
       contact that is in the user's roster with a subscription type of
       "from" or "both" after having sent initial presence and before
       sending unavailable presence broadcast (i.e., during the user's
       presence session), the user's server MUST locally deliver or
       remotely route the full XML of that presence stanza but SHOULD
       NOT otherwise modify the contact's status regarding presence
       broadcast (i.e., it SHOULD include the contact's JID in any
       subsequent presence broadcasts initiated by the user).
   2.  If the user sends directed presence to an entity that is not in
       the user's roster with a subscription type of "from" or "both"
       after having sent initial presence and before sending unavailable
       presence broadcast (i.e., during the user's presence session),
       the user's server MUST locally deliver or remotely route the full
       XML of that presence stanza to the entity but MUST NOT modify the
       contact's status regarding available presence broadcast (i.e., it
       MUST NOT include the entity's JID in any subsequent broadcasts of
       available presence initiated by the user); however, if the
       available resource from which the user sent the directed presence
       becomes unavailable, the user's server MUST route that
       unavailable presence to the entity (if the user has not yet sent
       directed unavailable presence to that entity).
   3.  If the user sends directed presence without first sending initial
       presence or after having sent unavailable presence broadcast
       (i.e., the resource is connected but not available), the user's
       server MUST treat the entity to which the user sends directed
       presence as in case #2 above.

4.6.3.  Server Processing of Inbound Directed Presence

   From the perspective of the contact's server, there is no difference
   between presence broadcast and directed presence, so the contact's
   server follows the existing rules for processing of inbound presence.



Saint-Andre              Expires October 2, 2010               [Page 57]

Internet-Draft                   XMPP IM                      March 2010


4.6.4.  Client Processing of Inbound Directed Presence

   When the contact's client receives directed presence from the user,
   it SHOULD proceed as follows:

   1.  If the user is in the contact's roster, the client MUST display
       the presence information in an appropriate roster interface.
   2.  If the user is not in the contact's roster but the contact and
       the user are actively exchanging message or IQ stanzas, the
       contact's client SHOULD display the presence information in the
       user interface for that chat session (see also Section 4.6 and
       Section 5.1).
   3.  Otherwise, the client MUST ignore the presence information and
       not display it to the contact.

4.7.  Presence Syntax

4.7.1.  Type Attribute

   The absence of a 'type' attribute signals that the relevant entity is
   available for communication (see Section 4.2 and Section 4.4).

   A 'type' attribute with a value of "unavailable" signals that the
   relevant entity is not available for communication (see Section 4.5).

   The XMPP presence stanza is also used to negotiate and manage
   subscriptions to the presence of other entities.  These tasks are
   completed via presence stanzas of type "subscribe", "unsubscribe",
   "subscribed", and "unsubscribed" as described under Section 3.

   If a user and contact are associated with different XMPP servers,
   those servers also use a special presence stanza of type "probe" in
   order to determine the availability of the entity on the peer server;
   for details, see Section 4.3.  Clients SHOULD NOT send presence
   stanzas of type "probe".

   The values of the 'type' attribute can be summarized as follows:

   o  error -- An error has occurred regarding processing of a
      previously-sent presence stanza; if the presence stanza is of type
      "error", it MUST include an <error/> child element (refer to
      [XMPP-CORE]).
   o  probe -- A request for an entity's current presence; SHOULD be
      generated only by a server on behalf of a user.
   o  subscribe -- The sender wishes to subscribe to the recipient's
      presence.





Saint-Andre              Expires October 2, 2010               [Page 58]

Internet-Draft                   XMPP IM                      March 2010


   o  subscribed -- The sender has allowed the recipient to receive
      their presence.
   o  unavailable -- Signals that the entity is no longer available for
      communication.
   o  unsubscribe -- The sender is unsubscribing from the receiver's
      presence.
   o  unsubscribed -- The subscription request has been denied or a
      previously-granted subscription has been cancelled.

   If the value of the 'type' attribute is not one of the foregoing
   values, the recipient or an intermediate router SHOULD return a
   stanza error of <bad-request/>.

      Note: There is no default value for the 'type' attribute of the
      <presence/> element; in particular, there is no value of
      "available".

4.7.2.  Child Elements

   In accordance with the default namespace declaration, a presence
   stanza is qualified by the 'jabber:client' or 'jabber:server'
   namespace, which defines certain allowable children of presence
   stanzas, in particular the <show/>, <status/>, and <priority/>
   elements.  These child elements are used to provide more detailed
   information about an entity's availability.  Typically these child
   elements are provided only if the presence stanza possesses no 'type'
   attribute, although exceptions are noted in the text that follows.

4.7.3.  Show Element

   The OPTIONAL <show/> element specifies the particular availability
   sub-state of an entity or a specific resource thereof.  A presence
   stanza MUST NOT contain more than one <show/> element.  There are no
   attributes defined for the <show/> element.  The XML character data
   of the <show/> element is not human-readable.  The XML character data
   MUST be one of the following (additional availability states could be
   defined through a child element of the presence stanza that is
   qualified by a namespace other than the default namespace):

   o  away -- The entity or resource is temporarily away.
   o  chat -- The entity or resource is actively interested in chatting.
   o  dnd -- The entity or resource is busy (dnd = "Do Not Disturb").
   o  xa -- The entity or resource is away for an extended period (xa =
      "eXtended Away").

   If no <show/> element is provided, the entity is assumed to be online
   and available.




Saint-Andre              Expires October 2, 2010               [Page 59]

Internet-Draft                   XMPP IM                      March 2010


   Any specialized processing of availability states by recipients and
   intermediate routers is up to the implementation (e.g., incorporation
   of availability states into stanza routing and delivery logic).

4.7.4.  Status Element

   The OPTIONAL <status/> element contains human-readable XML character
   data specifying a natural-language description of an entity's
   availability.  It is normally used in conjunction with the show
   element to provide a detailed description of an availability state
   (e.g., "In a meeting") when the presence stanza has no 'type'
   attribute.

   <presence from='romeo@example.net/orchard'
             xml:lang='en'>
     <show>dnd</show>
     <status>Wooing Juliet</status>
   </presence>

   There are no attributes defined for the <status/> element, with the
   exception of the 'xml:lang' attribute inherited from XML.  Multiple
   instances of the <status/> element MAY be included, but only if each
   instance possesses an 'xml:lang' attribute with a distinct language
   value (either explicitly or by inheritance from the 'xml:lang' value
   of an element farther up in the XML hierarchy, which can include the
   XML stream header as described in [XMPP-CORE]).

   <presence from='romeo@example.net/orchard'
             xml:lang='en'>
     <show>dnd</show>
     <status>Wooing Juliet</status>
     <status xml:lang='cs'>Dvo&#x0159;&#x00ED;m se Julii</status>
   </presence>

   A presence stanza of type "unavailable" MAY also include a <status/>
   element to provide detailed information about why the entity is going
   offline.

   <presence from='romeo@example.net/orchard'
             type='unavailable'
             xml:lang='en'>
     <status>Busy IRL</status>
   </presence>

   The <status/> child MAY also be sent in a subscription-related
   presence stanza (i.e., type "subscribe", "subscribed", "unsubscribe",
   or "unsubscribed") to provide a description of the action.  The
   receiving client MAY present this <status/> information to a human



Saint-Andre              Expires October 2, 2010               [Page 60]

Internet-Draft                   XMPP IM                      March 2010


   user (see Section 11).

   <presence from='romeo@example.net'
             to='nurse@example.com'
             type='subscribe'>
     <status>Hi, Juliet told to add you to my buddy list.</status>
   </presence>

4.7.5.  Priority Element

   The OPTIONAL <priority/> element contains non-human-readable XML
   character data that specifies the priority level of the resource.
   The value MUST be an integer between -128 and +127.  A presence
   stanza MUST NOT contain more than one <priority/> element.  There are
   no attributes defined for the <priority/> element.

   <presence xml:lang='en'>
     <show>dnd</show>
     <status>Wooing Juliet</status>
     <status xml:lang='cs'>Dvo&#x0159;&#x00ED;m se Julii</status>
     <priority>1</priority>
   </presence>

   If no priority is provided, the processing server or client MUST
   consider the priority to be zero ("0").

   The client's server MAY override the priority value provided by the
   client (e.g., in order to impose a message handling rule of
   delivering a message intended for the account's bare JID to all of
   the account's available resources); if the server does so, it MUST
   include the modified priority value (typically zero) when it echoes
   the client's presence back to itself.

   For information regarding the semantics of priority values in stanza
   processing within instant messaging and presence applications, refer
   to Section 8.

4.7.6.  Extended Content

   As described in [XMPP-CORE], an XML stanza MAY contain any child
   element that is qualified by a namespace other than the default
   namespace; this applies to the presence stanza as well.

   (In the following example, the presence stanza includes entity
   capabilities information as defined in [XEP-0115]).)






Saint-Andre              Expires October 2, 2010               [Page 61]

Internet-Draft                   XMPP IM                      March 2010


   <presence from='romeo@example.net'>
     <c xmlns='http://jabber.org/protocol/caps'
        hash='sha-1'
        node='http://psi-im.org'
        ver='q07IKJEyjvHSyhy//CH0CxmKi8w='/>
   </presence>

   Any extended content included in a presence stanza SHOULD represent
   aspects of an entity's availability for communication or provide
   information about communication-related capabilities.


5.  Exchanging Messages

   Once a client has authenticated with a server and bound a resource to
   an XML stream as described in [XMPP-CORE], an XMPP server will route
   XML stanzas to and from that client.  One kind of stanza that can be
   exchanged is <message/> (if, that is, messaging functionality is
   enabled and the server is not a presence-only service).  Exchanging
   messages is a basic use of XMPP and occurs when a user generates a
   message stanza that is addressed to another entity.  As defined under
   Section 8, the sender's server is responsible for delivering the
   message to the intended recipient (if the recipient is on the same
   local server) or for routing the message to the recipient's server
   (if the recipient is on a remote server).  Thus a message stanza is
   used to "push" information to another entity.

5.1.  One-to-One Chat Sessions

   In practice, instant messaging activity between human users tends to
   occur in form of a conversational burst that we call a CHAT SESSION:
   the exchange of at least several messages between two parties in
   relatively rapid succession within a relatively brief period of time.

   When a human user intends to engage in such a chat session with a
   contact (rather than sending a single message to which no reply is
   expected), the user's client SHOULD send a message of type "chat" and
   the contact's client SHOULD preserve that message type in subsequent
   replies.  The user's client also SHOULD include a <thread/> element
   with its initial message, which the contact's client SHOULD also
   preserve during the life of the chat session.

   The user's client MUST address the initial message in a chat session
   to the bare JID <contact@domain> of the contact (rather than
   attempting to guess an appropriate full JID <contact@domain/resource>
   based on the <show/>, <status/>, or <priority/> value of any presence
   notifications it has received from the contact).  Until and unless
   the user's client receives a reply from the contact, it MUST continue



Saint-Andre              Expires October 2, 2010               [Page 62]

Internet-Draft                   XMPP IM                      March 2010


   sending any further messages to the contact's bare JID.  The
   contact's client SHOULD address its subsequent replies to the user's
   full JID <user@domain/resource> as provided in the 'from' address of
   the initial message.  Once the user's client receives a reply from
   the contact's full JID, it SHOULD address its subsequent messages to
   the contact's full JID as provided in the 'from' address of the
   contact's replies, thus "locking in" on that full JID.

   When two parties engage in a chat session but do not share presence
   with each other based on a presence subscription, they SHOULD send
   directed presence to each other so that either party can easily
   discover if the peer changes its availability or goes offline during
   the course of the chat session.  However, a client MUST provide a way
   for a user to disable such presence sharing globally or to enable it
   only with particular entities.  Furthermore, a party SHOULD send
   directed unavailable to the peer when it has reason to believe that
   the chat session is over (e.g., if, after some reasonable amount of
   time, no subsequent messages have been exchanged between the
   parties).

   If a party receives a presence change from the peer during a one-to-
   one chat session (e.g., a new resource comes online or the existing
   resource sends modified presence), then it SHOULD address its next
   message(s) in the chat session to the bare JID of the peer (thus
   "unlocking" the previous "lock") until it receives a message from one
   of the peer's full JIDs.

   An example of a chat session is provided under Section 7.

5.2.  Message Syntax

   The following sections describe the syntax of the <message/> stanza.

5.2.1.  To Attribute

   An instant messaging client specifies an intended recipient for a
   message by providing the JID of an entity other than the sender in
   the 'to' attribute of the <message/> stanza.

   If the message is being sent outside the context of any existing chat
   session or received message, the value of the 'to' address SHOULD be
   of the form <user@domain> rather than of the form
   <user@domain/resource>.








Saint-Andre              Expires October 2, 2010               [Page 63]

Internet-Draft                   XMPP IM                      March 2010


   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <body>Art thou not Romeo, and a Montague?</body>
   </message>

   If the message is being sent in reply to a message previously
   received from an address of the form <user@domain/resource> (e.g.,
   within the context of a one-to-one chat session as described under
   Section 5.1), the value of the 'to' address SHOULD be of the form
   <user@domain/resource> rather than of the form <user@domain> unless
   the sender has knowledge (via presence) that the intended recipient's
   resource is no longer available.

   <message
       from='romeo@example.net/orchard'
       to='juliet@example.com/balcony'
       type='chat'
       xml:lang='en'>
     <body>Neither, fair saint, if either thee dislike.</body>
   </message>

5.2.2.  Type Attribute

   Common uses of the message stanza in instant messaging applications
   include: single messages; messages sent in the context of a one-to-
   one chat session; messages sent in the context of a multi-user chat
   room; alerts, notifications, or other information to which no reply
   is expected; and errors.  These uses are differentiated via the
   'type' attribute.  Inclusion of the 'type' attribute is RECOMMENDED.
   If included, the 'type' attribute MUST have one of the following
   values:

   o  chat -- The message is sent in the context of a one-to-one chat
      session.  Typically a receiving client will present message of
      type "chat" in an interface that enables one-to-one chat between
      the two parties, including an appropriate conversation history.
      Detailed recommendations regarding one-to-one chat sessions are
      provided under Section 5.1.
   o  error -- The message is generated by an entity that experiences an
      error in processing a message received from another entity (for
      details regarding stanza error syntax, refer to [XMPP-CORE]).  A
      client that receives a message of type "error" SHOULD present an
      appropriate interface informing the sender of the nature of the
      error.




Saint-Andre              Expires October 2, 2010               [Page 64]

Internet-Draft                   XMPP IM                      March 2010


   o  groupchat -- The message is sent in the context of a multi-user
      chat environment (similar to that of [IRC]).  Typically a
      receiving client will present a message of type "groupchat" in an
      interface that enables many-to-many chat between the parties,
      including a roster of parties in the chatroom and an appropriate
      conversation history.  For detailed information about XMPP-based
      groupchat, refer to [XEP-0045].
   o  headline -- The message provides an alert, a notification, or
      other information to which no reply is expected (e.g., news
      headlines, sports updates, near-real-time market data, and
      syndicated content).  Because no reply to the message is expected,
      typically a receiving client will present a message of type
      "headline" in an interface that appropriately differentiates the
      message from standalone messages, chat messages, or groupchat
      messages (e.g., by not providing the recipient with the ability to
      reply).  The receiving server SHOULD deliver the message to all of
      the recipient's available resources.
   o  normal -- The message is a standalone message that is sent outside
      the context of a one-to-one conversation or groupchat, and to
      which it is expected that the recipient will reply.  Typically a
      receiving client will present a message of type "normal" in an
      interface that enables the recipient to reply, but without a
      conversation history.  The default value of the 'type' attribute
      is "normal".

   An IM application SHOULD support all of the foregoing message types.
   If an application receives a message with no 'type' attribute or the
   application does not understand the value of the 'type' attribute
   provided, it MUST consider the message to be of type "normal" (i.e.,
   "normal" is the default).

   Although the 'type' attribute is OPTIONAL, it is considered polite to
   mirror the type in any replies to a message; furthermore, some
   specialized applications (e.g., a multi-user chat service) MAY at
   their discretion enforce the use of a particular message type (e.g.,
   type='groupchat').

5.2.3.  Body Element

   The <body/> element contains human-readable XML character data that
   specifies the textual contents of the message; this child element is
   normally included but is OPTIONAL.









Saint-Andre              Expires October 2, 2010               [Page 65]

Internet-Draft                   XMPP IM                      March 2010


   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <body>Wherefore art thou, Romeo?</body>
   </message>

   There are no attributes defined for the <body/> element, with the
   exception of the 'xml:lang' attribute.  Multiple instances of the
   <body/> element MAY be included in a message stanza, but only if each
   instance possesses an 'xml:lang' attribute with a distinct language
   value (either explicitly or by inheritance from the 'xml:lang' value
   of an element farther up in the XML hierarchy, which can include the
   XML stream header as described in [XMPP-CORE]).

   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <body>Wherefore art thou, Romeo?</body>
     <body xml:lang='cs'>
        Pro&#x010D;e&#x017D; jsi ty, Romeo?
      </body>
   </message>

   The <body/> element MUST NOT contain mixed content (as defined in
   Section 3.2.2 of [XML]).

5.2.4.  Subject Element

   The <subject/> element contains human-readable XML character data
   that specifies the topic of the message.

   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <subject>I implore you!</subject>
     <body>Wherefore art thou, Romeo?</body>
   </message>

   There are no attributes defined for the <subject/> element, with the
   exception of the 'xml:lang' attribute inherited from XML.  Multiple
   instances of the <subject/> element MAY be included for the purpose
   of providing alternate versions of the same subject, but only if each



Saint-Andre              Expires October 2, 2010               [Page 66]

Internet-Draft                   XMPP IM                      March 2010


   instance possesses an 'xml:lang' attribute with a distinct language
   value (either explicitly or by inheritance from the 'xml:lang' value
   of an element farther up in the XML hierarchy, which can include the
   XML stream header as described in [XMPP-CORE]).

   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <subject>I implore you!</subject>
     <subject xml:lang='cs'>
       &#x00DA;p&#x011B;nliv&#x011B; pros&#x00ED;m!
     </subject>
     <body>Wherefore art thou, Romeo?</body>
     <body xml:lang='cs'>
        Pro&#x010D;e&#x017E; jsi ty, Romeo?
      </body>
   </message>

   The <subject/> element MUST NOT contain mixed content (as defined in
   Section 3.2.2 of [XML]).

5.2.5.  Thread Element

   The primary use of the XMPP <thread/> element is to uniquely identify
   a conversation thread or "chat session" between two entities
   instantiated by <message/> stanzas of type 'chat'.  However, the XMPP
   <thread/> element can also be used to uniquely identify an analogous
   thread between two entities instantiated by <message/> stanzas of
   type 'headline' or 'normal', or among multiple entities in the
   context of a multi-user chat room instantiated by <message/> stanzas
   of type 'groupchat'.  It MAY also be used for <message/> stanzas not
   related to a human conversation, such as a game session or an
   interaction between plugins.  The <thread/> element is not used to
   identify individual messages, only conversations or messagingg
   sessions.

   The inclusion of the <thread/> element is OPTIONAL.  Because the
   <thread/> element uniquely identifies the particular conversation
   thread to which a message belongs, a message stanza MUST NOT contain
   more than one <thread/> element.

   The value of the <thread/> element is not human-readable and MUST be
   treated as opaque by entities; no semantic meaning can be derived
   from it, and only exact comparisons can be made against it.  The
   value of the <thread/> element MUST be a universally unique
   identifier (UUID) as described in [UUID].



Saint-Andre              Expires October 2, 2010               [Page 67]

Internet-Draft                   XMPP IM                      March 2010


   The <thread/> element MAY possess a 'parent' attribute that
   identifies another thread of which the current thread is an offshoot
   or child; the value of the 'parent' MUST conform to the syntax of the
   <thread/> element itself.

   The <thread/> element MUST NOT contain mixed content (as defined in
   Section 3.2.2 of [XML]).

   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <subject>I implore you!</subject>
     <subject xml:lang='cs'>
       &#x00DA;p&#x011B;nliv&#x011B; pros&#x00ED;m!
     </subject>
     <body>Wherefore art thou, Romeo?</body>
     <body xml:lang='cs'>
        Pro&#x010D;e&#x017E; jsi ty, Romeo?
     </body>
     <thread parent='e0ffe42b28561960c6b12b944a092794b9683a38'>
       0e3141cd80894871a68e6fe6b1ec56fa
     </thread>
   </message>

   For detailed recommendations regarding use of the <thread/> element,
   refer to [XEP-0201].

5.3.  Extended Content

   As described in [XMPP-CORE], an XML stanza MAY contain any child
   element that is qualified by a namespace other than the default
   namespace; this applies to the message stanza as well.

   (In the following example, the message stanza includes an XHTML-
   formatted version of the message as defined in [XEP-0071]).)














Saint-Andre              Expires October 2, 2010               [Page 68]

Internet-Draft                   XMPP IM                      March 2010


   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <body>Wherefore art thou, Romeo?</body>
     <html xmlns='http://jabber.org/protocol/xhtml-im'>
       <body xmlns='http://www.w3.org/1999/xhtml'>
         Wherefore <span style='font-style: italic'>art</span>
         thou, <span style='color:red'>Romeo</span>?
       </body>
     </html>
   </message>


6.  Exchanging IQ Stanzas

   As described in [XMPP-CORE], IQ stanzas provide a structured request-
   response mechanism.  The basic semantics of that mechanism (e.g.,
   that the 'id' attribute is mandatory) are defined in [XMPP-CORE],
   whereas the specific semantics needed to complete particular use
   cases are defined in all instances by the extended namespace that
   qualifies the direct child element of an IQ stanza of type "get" or
   "set".  The 'jabber:client' and 'jabber:server' namespaces do not
   define any children of IQ stanzas other than the <error/> element
   common to all stanza types.  This document defines one such extended
   namespace, for Managing the Roster (Section 2).  However, an IQ
   stanza MAY contain structured information qualified by any extended
   namespace.

   As noted under Section 4.6, if a user exchanges IQ stanzas with
   another entity but does not share presence with the entity based on a
   presence subscription, it is RECOMMENDED for the user's client to
   send directed presence to the other entity.


7.  A Sample Session

   The examples in this section illustrate a possible instant messaging
   and presence session.  The user is romeo@example.net, he has an
   available resource whose resource identifier is "orchard", and he has
   the following individuals in his roster:

   o  juliet@example.com (subscription="both" and she has two available
      resources, one whose resource identifier is "chamber" and another
      whose resource identifier is "balcony")





Saint-Andre              Expires October 2, 2010               [Page 69]

Internet-Draft                   XMPP IM                      March 2010


   o  benvolio@example.net (subscription="to")
   o  mercutio@example.org (subscription="from")

   First, the user completes the preconditions (stream establishment,
   TLS and SASL negotiation, and resource binding) described in
   [XMPP-CORE]; those protocol flows are not reproduced here.

   Next, the user requests his roster.

   Example 1: User requests current roster from server:

   UC: <iq from='romeo@example.net/balcony'
           id='ex1'
           type='get'>
         <query xmlns='jabber:iq:roster'/>
       </iq>

   Example 2: User receives roster from server:

   US: <iq to='romeo@example.net/balcony'
           id='ex1'
           type='result'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 name='Juliet'
                 subscription='both'>
             <group>Friends</group>
           </item>
           <item jid='benvolio@example.org'
                 name='Benvolio'
                 subscription='to'/>
           <item jid='mercutio@example.org'
                 name='Mercutio'
                 subscription='from'/>
         </query>
       </iq>

   Now the user begins a presence session.

   Example 3: User sends initial presence:

   UC: <presence from='romeo@example.net/orchard'/>









Saint-Andre              Expires October 2, 2010               [Page 70]

Internet-Draft                   XMPP IM                      March 2010


   Example 4: User's server sends presence probes to contacts with
   subscription="to" and subscription="both" on behalf of the user's
   available resource:

   US: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'
           type='probe'/>

   US: <presence
           from='romeo@example.net/orchard'
           to='benvolio@example.org'
           type='probe'/>

   Example 5: User's server sends initial presence to contacts with
   subscription="from" and subscription="both" on behalf of the user's
   available resource:

   US: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'/>

   US: <presence
           from='romeo@example.net/orchard'
           to='mercutio@example.org'/>


























Saint-Andre              Expires October 2, 2010               [Page 71]

Internet-Draft                   XMPP IM                      March 2010


   Example 6: Contacts' servers reply to presence probe on behalf of all
   available resources:

   CS: <presence
           from='juliet@example.com/balcony'
           to='romeo@example.net/orchard'
           xml:lang='en'>
         <show>away</show>
         <status>be right back</status>
         <priority>0</priority>
       </presence>

   CS: <presence
           from='juliet@example.com/chamber'
           to='romeo@example.net/orchard'>
         <priority>1</priority>
       </presence>

   CS: <presence
           from='benvolio@example.org/pda'
           to='romeo@example.net/orchard'
           xml:lang='en'>
         <show>dnd</show>
         <status>gallivanting</status>
       </presence>

   Example 7: Contacts' servers deliver user's initial presence to all
   available resources:

   CS: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'/>

   CS: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'/>

   CS: <presence
           from='mercutio@example.org'
           to='romeo@example.net'/>











Saint-Andre              Expires October 2, 2010               [Page 72]

Internet-Draft                   XMPP IM                      March 2010


   Example 8: User sends directed presence to another user not in his
   roster:

   UC: <presence
           from='romeo@example.net/orchard'
           to='nurse@example.com'
           xml:lang='en'>
         <show>dnd</show>
         <status>courting Juliet</status>
         <priority>0</priority>
       </presence>

   Now the user engages in a chat session with one of his contacts.






































Saint-Andre              Expires October 2, 2010               [Page 73]

Internet-Draft                   XMPP IM                      March 2010


   Example 9: A threaded conversation

   CC: <message
           from='juliet@example.com/balcony'
           to='romeo@example.net'
           type='chat'
           xml:lang='en'>
         <body>My ears have not yet drunk a hundred words</body>
         <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
       </message>

   CC: <message
           from='juliet@example.com/balcony'
           to='romeo@example.net'
           type='chat'
           xml:lang='en'>
         <body>Of that tongue's utterance, yet I know the sound:</body>
         <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
       </message>

   CC: <message
           from='juliet@example.com/balcony'
           to='romeo@example.net'
           type='chat'
           xml:lang='en'>
         <body>Art thou not Romeo, and a Montague?</body>
         <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
       </message>

   UC: <message
           from='romeo@example.net/orchard'
           to='juliet@example.com/balcony'
           type='chat'
           xml:lang='en'>
         <body>Neither, fair saint, if either thee dislike.</body>
         <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
       </message>

   CC: <message
           from='juliet@example.com/balcony'
           to='romeo@example.net/orchard'
           type='chat'
           xml:lang='en'>
         <body>How cam'st thou hither, tell me, and wherefore?</body>
         <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
       </message>

   And so on.



Saint-Andre              Expires October 2, 2010               [Page 74]

Internet-Draft                   XMPP IM                      March 2010


   The user can also send subsequent presence broadcast.

   Example 10: User sends updated available presence for broadcasting:

   UC: <presence xml:lang='en'>
         <show>away</show>
         <status>I shall return!</status>
         <priority>1</priority>
       </presence>

   Example 11: User's server broadcasts updated presence only to one
   contact:

   US: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'
           xml:lang='en'>
         <show>away</show>
         <status>I shall return!</status>
         <priority>1</priority>
       </presence>

   Example 12: Contact's server delivers updated presence to all of the
   contact's available resources ("balcony" and "chamber"):

   CS: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'
           xml:lang='en'>
         <show>away</show>
         <status>I shall return!</status>
         <priority>1</priority>
       </presence>

   CS: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'
           xml:lang='en'>
         <show>away</show>
         <status>I shall return!</status>
         <priority>1</priority>
       </presence>

   Example 13: One of the contact's resources broadcasts unavailable
   notification:

   CC: <presence from='juliet@example.com/chamber' type='unavailable'/>




Saint-Andre              Expires October 2, 2010               [Page 75]

Internet-Draft                   XMPP IM                      March 2010


   Example 14: Contact's server sends unavailable notification to user:

   CS: <presence
           from='juliet@example.com/chamber'
           to='romeo@example.net'
           type='unavailable'/>

   Now the user ends his presence session.

   Example 15: User sends unavailable notification:

   UC: <presence from='romeo@example.net/orchard'
                 type='unavailable'
                 xml:lang='en'>
         <status>gone home</status>
       </presence>

   Example 16: User's server broadcasts unavailable notification to
   contacts as well as to the person to whom the user sent directed
   presence:

   US: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'
           type='unavailable'
           xml:lang='en'>
         <status>gone home</status>
       </presence>

   US: <presence
           from='romeo@example.net/orchard'
           to='nurse@example.com'
           type='unavailable'
           xml:lang='en'>
         <status>gone home</status>
       </presence>

   Finally the user closes his stream and the server responds in kind.

   Example 17: User closes stream:

   UC: </stream:stream>

   Example 18: User's server closes stream:

   US: </stream:stream>

   THE END



Saint-Andre              Expires October 2, 2010               [Page 76]

Internet-Draft                   XMPP IM                      March 2010


8.  Server Rules for Processing XML Stanzas

   Basic server rules for processing XML stanzas are defined in
   [XMPP-CORE].  This section defines supplementary rules for XMPP
   instant messaging and presence servers; in the absence of a
   supplementary rule defined below (e.g., for stanzas without a 'to'
   address), the rule defined in [XMPP-CORE] applies.

8.1.  No Such User

   If the user account identified by the 'to' attribute does not exist,
   how the stanza is processed depends on the stanza type.

   o  For an IQ stanza, the server MUST return a <service-unavailable/>
      stanza error to the sender.
   o  For a message stanza, the server MUST return a <service-
      unavailable/> stanza error to the sender.
   o  For a presence stanza with no 'type' attribute or a 'type'
      attribute of "unavailable", the server MUST silently ignore the
      stanza.
   o  For a presence stanza of type "subscribe", the server MUST return
      a presence stanza of type "unsubscribed".
   o  For a presence stanza of type "subscribed", "unsubscribe", or
      "unsubscribed", the server MUST silently ignore the stanza.
   o  For a presence stanza of type "probe", the server MUST return a
      presence stanza of type "unsubscribed".

8.2.  Full JID at Local Domain

   If the hostname of the domain identifier portion of the JID contained
   in the 'to' attribute of an inbound stanza matches one of the
   configured hostnames of the server itself and the JID contained in
   the 'to' attribute is of the form <user@domain/resource>, then the
   server MUST adhere to the following rules (subject to enforcement of
   relevant privacy and security policies, such as those deployed by
   means of [XEP-0016] or [XEP-0191]).

8.2.1.  Resource Matches

   If an available or connected resource exactly matches the full JID,
   how the stanza is processed depends on the stanza type.

   o  For an IQ stanzas of type "get" or "set", if the intended
      recipient does not share presence with the requesting entity
      either by means of a presence subscription of type "both" or
      "from" or by means of directed presence, then the server SHOULD
      NOT deliver the IQ stanza but instead SHOULD return a <service-
      unavailable/> stanza error to the requesting entity.  This policy



Saint-Andre              Expires October 2, 2010               [Page 77]

Internet-Draft                   XMPP IM                      March 2010


      helps to prevent presence leaks (see Section 11).
   o  For a message stanza, the server MUST deliver the stanza to the
      resource.
   o  For a presence stanza with no 'type' attribute or a 'type'
      attribute of "unavailable", the server MUST deliver the stanza to
      the resource.
   o  For a presence stanza of type "subscribe", the server MUST follow
      the guidelines provided under Section 3.1.3.
   o  For a presence stanza of type "subscribe", "subscribed",
      "unsubscribe", or "unsubscribed", the server MUST follow the
      guidelines provided under Section 3.
   o  For a presence stanza of type "probe", the server MUST follow the
      guidelines provided under Section 4.3.

8.2.2.  No Resource Matches

   If no connected or available resource exactly matches the full JID,
   how the stanza is processed depends on the stanza type.

   o  For an IQ stanza, the server MUST return a <service-unavailable/>
      stanza error to the sender.
   o  For a message stanza of type "chat", "headline", or "normal", the
      server SHOULD treat the stanza as if it were addressed to
      <user@domain> as described in the next section (but without
      modifying the value of the 'to' attribute).
   o  For a message stanza of type "error", the server MUST silently
      ignore the stanza.
   o  For a message stanza of type "groupchat", the server MUST return a
      stanza error to the sender, which SHOULD be <service-
      unavailable/>.
   o  For a presence stanza with no 'type' attribute or a 'type'
      attribute of "unavailable", the server MUST silently ignore the
      stanza.
   o  For a presence stanza of type "subscribe", the server MUST follow
      the guidelines provided under Section 3.1.3.
   o  For a presence stanza of type "subscribed", "unsubscribe", or
      "unsubscribed", the server MUST ignore the stanza.
   o  For a presence stanza of type "probe", the server MUST follow the
      guidelines provided under Section 4.3.

8.3.  Bare JID at Local Domain

   If the hostname of the domain identifier portion of the JID contained
   in the 'to' attribute of an inbound stanza matches one of the
   configured hostnames of the server itself and the JID contained in
   the 'to' attribute is of the form <user@domain>, then the server MUST
   adhere to the following rules.




Saint-Andre              Expires October 2, 2010               [Page 78]

Internet-Draft                   XMPP IM                      March 2010


8.3.1.  Available or Connected Resources

   If there is at least one available or connected resource, how the
   stanza is processed depends on the stanza type.

8.3.1.1.  Message

   For a message stanza of type "headline", the server MUST deliver the
   stanza to all available resources.

   For a message stanza of type "chat" or "normal", the server MUST
   either (a) deliver the stanza to the highest-priority available
   resource(s), or (b) deliver the stanza to all available resources
   with non-negative presence priority.  In the case of (a), if there is
   not one highest-priority available resource but instead the highest
   priority is asserted by two or more available resources, these
   resources are said to form a "delivery tie".  If there is a delivery
   tie, a server SHOULD deliver the message to all of the tied
   resources.  However, before delivering the message, a server MAY
   remove one or more resources from the tie.  Methods for doing so are
   outside the scope of this specification, but could include factors
   such as the resource's time of connection, time of last network or
   application activity, availability as determined by some hierarchy of
   <show/> values, or user-configured rules.  Nevertheless, a server
   MUST NOT remove all resources from the tie, and MUST deliver the
   message to at least one of the highest-priority resources (subject to
   appropriate security policies as described under Section 11 and in
   [XMPP-CORE]).

   For a message stanza of type "groupchat", the server MUST NOT deliver
   the stanza to any of the available resources but instead MUST return
   a stanza error to the sender, which SHOULD be <service-unavailable/>.

   For a message stanza of type "error", the server MUST silently
   discard the message (i.e., neither deliver it to the intended
   recipient nor return a stanza error to the sender).

   However, for any message type the server MUST NOT deliver the stanza
   to any available resource with a negative priority; if the only
   available resource has a negative priority, the server SHOULD handle
   the message as if there were no available or connected resources as
   described under Section 8.3.2.

   In all cases, the server MUST NOT rewrite the 'to' attribute (i.e.,
   it MUST leave it as <user@domain> rather than change it to
   <user@domain/resource>).





Saint-Andre              Expires October 2, 2010               [Page 79]

Internet-Draft                   XMPP IM                      March 2010


8.3.1.2.  Presence

   For a presence stanza with no type or of type "unavailable", the
   server MUST deliver it to all available resources.

   For a presence stanza of type "subscribe", "subscribed",
   "unsubscribe", or "unsubscribed", the server MUST adhere to the rules
   defined under Section 3 and summarized under Appendix A.

   For a presence stanza of type "probe", the server MUST handle it
   directly as described under Section 4.3.

   In all cases, the server MUST NOT rewrite the 'to' attribute (i.e.,
   it MUST leave it as <user@domain> rather than change it to
   <user@domain/resource>).

8.3.1.3.  IQ

   For an IQ stanza, the server itself MUST reply on behalf of the user
   with either an IQ result or an IQ error, and MUST NOT deliver the IQ
   stanza to any of the user's available resources.  Specifically, if
   the semantics of the qualifying namespace define a reply that the
   server can provide on behalf of the user, then the server MUST reply
   to the stanza on behalf of the user by returning either an IQ stanza
   of type "result" or an IQ stanza of type "error" that is appropriate
   to the original payload; if not, then the server MUST reply with a
   <service-unavailable/> stanza error.

8.3.2.  No Available or Connected Resources

   If there are no available or connected resources associated with the
   user, how the stanza is processed depends on the stanza type.

8.3.2.1.  Message

   In order to properly handle message stanzas, it is RECOMMENDED for an
   implementation to support OFFLINE STORAGE, i.e., the server SHOULD
   store the message stanza on behalf of the user and deliver it when
   the user next becomes available.  For recommendations regarding
   offline message storage refer to [XEP-0160].

   For a message stanza of type "chat" or "normal", the server SHOULD
   add the message to offline storage or forward the message to the user
   via a non-XMPP messaging system (e.g., to the user's email account).
   However, if offline message storage or message forwarding is not
   enabled or available (e.g., because a size limit has been reached on
   offline messages), then the server MUST return a <service-
   unavailable/> stanza error to the sender.



Saint-Andre              Expires October 2, 2010               [Page 80]

Internet-Draft                   XMPP IM                      March 2010


   For a message stanza of type "headline", according to local service
   policies the server MUST either (a) add the message to offline
   storage or (b) silently discard the message (i.e., neither deliver it
   to the intended recipient nor return an error to the sender).

   For a message stanza of type "groupchat", the server SHOULD NOT add
   the message to offline storage but instead SHOULD return an error to
   the sender.

   For a message stanza of type "error", the server MUST NOT add the
   message to offline storage but instead MUST silently discard the
   message (i.e., neither deliver it to the intended recipient nor
   return an error to the sender).

8.3.2.2.  Presence

   For a presence stanza with no type or of type "unavailable", the
   server SHOULD silently ignore the stanza by not storing it for later
   delivery and not replying to it on behalf of the user.

   For a presence stanza of type "subscribe", "subscribed",
   "unsubscribe", or "unsubscribed", the server MUST adhere to the rules
   defined under Section 3 and summarized under Appendix A.

   For a presence stanza of type "probe", the server MUST handle it
   directly as described under Section 4.3.

8.3.2.3.  IQ

   For an IQ stanza, the server itself MUST reply on behalf of the user
   with either an IQ result or an IQ error.  Specifically, if the
   semantics of the qualifying namespace define a reply that the server
   can provide on behalf of the user, then the server MUST reply to the
   stanza on behalf of the user by returning either an IQ stanza of type
   "result" or an IQ stanza of type "error" that is appropriate to the
   original payload; if not, then the server MUST reply with a <service-
   unavailable/> stanza error.

8.4.  Remote Domain

   If the hostname of the domain identifier portion of the address
   contained in the 'to' attribute of an outbound stanza does not match
   a configured hostname of the server itself, then the server MUST
   attempt to route the stanza to the remote domain.  If there exists an
   active stream between the two peers, then the server MUST route the
   stanza over that stream for processing by the peer server.  If not,
   then the server MUST do the following.




Saint-Andre              Expires October 2, 2010               [Page 81]

Internet-Draft                   XMPP IM                      March 2010


   First, resolve the hostname of the remote domain (or use a cached
   resolution of the remote domain to an IP address).  The RECOMMENDED
   order of attempted resolutions is as follows:

   1.  Attempt to resolve the remote hostname using a DNS service
       location record [SRV] Service of "xmpp-server" and a Proto of
       "tcp", resulting in resource records such as "_xmpp-
       server._tcp.example.com.", as specified in [XMPP-CORE].
   2.  If the "xmpp-server" address record resolution fails, attempt to
       resolve the "_im" or "_pres" SRV Service as specified in
       [IMP-SRV], using the "_im" Service for <message/> stanzas and the
       "_pres" Service for <presence/> stanzas (it is up to the
       implementation how to handle <iq/> stanzas).  This will result in
       one or more resolutions of the form "_im.<proto>.example.com." or
       "_pres.<proto>.example.com.", where "<proto>" would be a label
       registered in the Instant Messaging SRV Protocol Label registry
       or the Presence SRV Protocol Label registry: either "_xmpp" for
       an XMPP-aware domain or some other IANA-registered label (e.g.,
       "_simple") for a non-XMPP-aware domain.
   3.  If both SRV address record resolutions fail, attempt to perform a
       normal IPv4/IPv6 address record resolution to determine the IP
       address using the "xmpp-server" port of 5269 registered with the
       IANA, as specified in [XMPP-CORE].

   If the server cannot resolve the remote domain, it MUST return a
   <remote-server-not-found/> stanza error.

   Second, negotiate XML streams with the remote domain by following the
   process defined in [XMPP-CORE].  If the server can resolve the remote
   domain but cannot establish streams with the XMPP service at that
   domain, it MUST return a <remote-server-timeout/> stanza error.

   Third, route the stanza to the remote domain for processing by the
   peer server.

      Note: Administrators of server deployments are strongly encouraged
      to keep the _im._xmpp, _pres._xmpp, and _xmpp._tcp SRV records
      properly synchronized, since different implementations might
      perform the "_im" and "_pres" lookups before the "xmpp-server"
      lookup.


9.  Handling of URIs

   The addresses of XMPP entities as used in communication over an XMPP
   network (e.g., in the 'from' and 'to' addresses of an XML stanza)
   MUST NOT be prepended with a Uniform Resource Identifier [URI]
   scheme.  However, an application that is external to XMPP itself



Saint-Andre              Expires October 2, 2010               [Page 82]

Internet-Draft                   XMPP IM                      March 2010


   (e.g., a page on the World Wide Web) might need to identify an XMPP
   entity either as a URI or as an Internationalized Resource Identifier
   [IRI], and an XMPP client might need to interact with such an
   external application (for example, an XMPP client might be invoked by
   clicking a link provided on a web page).

   In the context of such interactions, an XMPP client SHOULD handle
   addresses that are encoded as "xmpp:" URIs and IRIs as specified in
   [XMPP-URI] and further described in [XEP-0147].  A client SHOULD also
   handle addresses that are encoded as "im:" URIs as specified in
   [CPIM] and "pres:" URIs as specified in [CPP], although it MAY do so
   by removing the "im:" or "pres:" scheme and entrusting address
   resolution to the server as specified under Section 8.4.


10.  Internationalization Considerations

   For internationalization considerations, refer to the relevant
   section of [XMPP-CORE].


11.  Security Considerations

   Core security considerations for XMPP are defined in the relevant
   section of [XMPP-CORE].

   Additional considerations that apply only to instant messaging and
   presence applications of XMPP are defined in several places within
   this document; specifically:

   o  When a server processes an inbound presence stanza of type "probe"
      whose intended recipient is a user associated with one of the
      server's hostnames, the server MUST NOT reveal the user's presence
      if the sender is an entity that is not authorized to receive that
      information as determined by presence subscriptions (see
      Section 4).
   o  A user's server MUST NOT leak the user's network availability to
      entities who are not authorized to know the user's presence,
      either via an explicit subscription as described herein or via an
      existing trust relationship (such as presence-enabled user
      directories within organizations).
   o  When a server processes an outbound presence stanza with no type
      or of type "unavailable", it MUST follow the rules defined under
      Section 4 in order to ensure that such presence information is not
      sent to entities that are not authorized to know such information.
   o  A client MAY ignore the <status/> element when contained in a
      presence stanza of type "subscribe", "unsubscribe", "subscribed",
      or "unsubscribed"; this can help prevent "presence subscription



Saint-Andre              Expires October 2, 2010               [Page 83]

Internet-Draft                   XMPP IM                      March 2010


      spam".


12.  IANA Considerations

   The following sections update the registrations provided in
   [RFC3921].

   For a number of related IANA considerations, refer to the relevant
   section of [XMPP-CORE].

12.1.  Instant Messaging SRV Protocol Label Registration

   Address Resolution for Instant Messaging and Presence [IMP-SRV]
   defines an Instant Messaging SRV Protocol Label registry for
   protocols that can provide services that conform to the "_im" SRV
   Service label.  Because XMPP is one such protocol, the IANA registers
   the "_xmpp" protocol label in the appropriate registry, as follows:

   Protocol label:  _xmpp
   Specification:  XXXX
   Description:  Instant messaging protocol label for the Extensible
      Messaging and Presence Protocol (XMPP) as defined by XXXX.
   Registrant Contact:  IETF, XMPP Working Group, <xmppwg@xmpp.org>

12.2.  Presence SRV Protocol Label Registration

   Address Resolution for Instant Messaging and Presence [IMP-SRV]
   defines a Presence SRV Protocol Label registry for protocols that can
   provide services that conform to the "_pres" SRV Service label.
   Because XMPP is one such protocol, the IANA registers the "_xmpp"
   protocol label in the appropriate registry, as follows:

   Protocol label:  _xmpp
   Specification:  XXXX
   Description:  Presence protocol label for the Extensible Messaging
      and Presence Protocol (XMPP) as defined by XXXX.
   Registrant Contact:  IETF, XMPP Working Group, <xmppwg@xmpp.org>


13.  Conformance Requirements

   This section describes a protocol feature set that summarizes the
   conformance requirements of this specification.  This feature set is
   appropriate for use in software certification, interoperability
   testing, and implementation reports.  For each feature, this section
   provides the following information:




Saint-Andre              Expires October 2, 2010               [Page 84]

Internet-Draft                   XMPP IM                      March 2010


   o  A human-readable name
   o  An informational description
   o  A reference to the particular section of this document that
      normatively defines the feature
   o  Whether the feature applies to the Client role, the Server role,
      or both (where "N/A" signifies that the feature is not applicable
      to the specified role)
   o  Whether the feature MUST or SHOULD be implemented, where the
      capitalized terms are to be understood as described in [TERMS]

   Note: The feature set specified here attempts to adhere to the
   concepts and formats proposed by Larry Masinter within the IETF's
   NEWTRK Working Group in 2005, as captured in [INTEROP].  Although
   this feature set is more detailed than called for by [REPORTS], it
   provides a suitable basis for the generation of implementation
   reports to be submitted in support of advancing this specification
   from Proposed Standard to Draft Standard in accordance with
   [PROCESS].

   Feature:  message-body
   Description:  Support the <body/> child element of the <message/>
      stanza.
   Section:  Section 5.2.3
   Roles:  Client MUST, Server N/A.

   Feature:  message-subject
   Description:  Support the <subject/> child element of the <message/>
      stanza.
   Section:  Section 5.2.4
   Roles:  Client SHOULD, Server N/A.

   Feature:  message-thread
   Description:  Support the <thread/> child element of the <message/>
      stanza.
   Section:  Section 5.2.5
   Roles:  Client SHOULD, Server N/A.

   Feature:  message-type
   Description:  Differentiate between messages of type "normal",
      "chat", "groupchat", "headline", and "error".
   Section:  Section 5.2.2
   Roles:  Client MUST, Server N/A.

   Feature:  presence-notype







Saint-Andre              Expires October 2, 2010               [Page 85]

Internet-Draft                   XMPP IM                      March 2010


   Description:  Treat a presence stanza with no 'type' attribute as
      indicating availability.
   Section:  Section 4.7.1
   Roles:  Client MUST, Server MUST.

   Feature:  presence-probe
   Description:  Send and receive presence stanzas with a 'type'
      attribute of "probe" for the discovery of presence information.
   Section:  Section 4.7.1
   Roles:  Client N/A, Server MUST.

   Feature:  presence-sub-approval
   Description:  Treat an outbound presence stanza of type "subscribed"
      as the act of approving a presence subscription request previously
      received from another entity, and treat an inbound presence stanza
      of type "subscribed" as a subscription approval from another
      entity.
   Section:  Section 3.1
   Roles:  Client MUST, Server MUST.

   Feature:  presence-sub-cancel
   Description:  Treat an outbound presence stanza of type
      "unsubscribed" as the act of denying a subscription request
      received from another entity or cancelling a subscription approval
      previously granted to another entity, and treat an inbound
      presence stanza of type "unsubscribed" as an subscription denial
      or cancellation from another entity.
   Section:  Section 3.2
   Roles:  Client MUST, Server MUST.

   Feature:  presence-sub-request
   Description:  Treat an outbound presence stanza of type "subscribe"
      as the act of requesting a subscription to the presence
      information of another entity, and treat an inbound presence
      stanza of type "subscribe" as a presence subscription request from
      another entity.
   Section:  Section 3.1
   Roles:  Client MUST, Server MUST.

   Feature:  presence-sub-unsubscribe
   Description:  Treat an outbound presence stanza of type "unsubscribe"
      as the act of unsubscribing from another entity, and treat an
      inbound presence stanza of type "unsubscribe" as an unsubscribe
      notification from another entity.







Saint-Andre              Expires October 2, 2010               [Page 86]

Internet-Draft                   XMPP IM                      March 2010


   Section:  Section 3.3
   Roles:  Client MUST, Server MUST.

   Feature:  presence-unavailable
   Description:  Treat a presence stanza with a 'type' attribute of
      "unavailable" as indicating lack of availability.
   Section:  Section 4.7.1
   Roles:  Client MUST, Server MUST.

   Feature:  roster-get
   Description:  Treat an IQ stanza of type "get" containing an empty
      <query/> element qualified by the 'jabber:iq:roster' namespace as
      a request to retrieve the roster information associated with an
      account on a server.
   Section:  Section 2.1.3
   Roles:  Client MUST, Server MUST.

   Feature:  roster-set
   Description:  Treat an IQ stanza of type "set" containing a <query/>
      element qualified by the 'jabber:iq:roster' namespace as a request
      to add or update the item contained in the <query/> element.
   Section:  Section 2.1.4
   Roles:  Client MUST, Server MUST.

   Feature:  roster-push
   Description:  Send a roster push to each interested resource whenever
      the server-side representation of the roster information
      materially changes, or handle such a push when received from the
      server.
   Section:  Section 2.1.5
   Roles:  Client MUST, Server MUST.

   Feature:  roster-version
   Description:  Treat the 'ver' attribute of the <query/> element
      qualified by the 'jabber:iq:roster' namespace as an identifier of
      the particular version of roster information being sent or
      received.
   Section:  Section 2.1.1
   Roles:  Client MUST, Server MUST.


14.  References

14.1.  Normative References

   [IMP-SRV]  Peterson, J., "Address Resolution for Instant Messaging
              and Presence", RFC 3861, August 2004.




Saint-Andre              Expires October 2, 2010               [Page 87]

Internet-Draft                   XMPP IM                      March 2010


   [XMPP-CORE]
              Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", draft-ietf-xmpp-3920bis-06 (work
              in progress), March 2010.

   [SRV]      Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [TERMS]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [UUID]     Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              July 2005.

   [XML]      Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F.,
              and T. Bray, "Extensible Markup Language (XML) 1.0 (Fourth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20060816, August 2006,
              <http://www.w3.org/TR/2006/REC-xml-20060816>.

   [XML-NAMES]
              Bray, T., Hollander, D., and A. Layman, "Namespaces in
              XML", W3C REC-xml-names, January 1999,
              <http://www.w3.org/TR/REC-xml-names>.

   [XMPP-URI]
              Saint-Andre, P., "Internationalized Resource Identifiers
              (IRIs) and Uniform Resource Identifiers (URIs) for the
              Extensible Messaging and Presence Protocol (XMPP)",
              RFC 5122, February 2008.

14.2.  Informative References

   [CPIM]     Peterson, J., "Common Profile for Instant Messaging
              (CPIM)", RFC 3860, August 2004.

   [CPP]      Peterson, J., "Common Profile for Presence (CPP)",
              RFC 3859, August 2004.

   [DELAY]    Saint-Andre, P., "Delayed Delivery", XSF XEP 0203,
              September 2009.

   [IMP-MODEL]
              Day, M., Rosenberg, J., and H. Sugano, "A Model for
              Presence and Instant Messaging", RFC 2778, February 2000.




Saint-Andre              Expires October 2, 2010               [Page 88]

Internet-Draft                   XMPP IM                      March 2010


   [IMP-REQS]
              Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging
              / Presence Protocol Requirements", RFC 2779,
              February 2000.

   [INTEROP]  Masinter, L., "Formalizing IETF Interoperability
              Reporting", draft-ietf-newtrk-interop-reports-00 (work in
              progress), October 2005.

   [IRC]      Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
              April 2000.

   [IRI]      Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [PROCESS]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [REPORTS]  Dusseault, L. and R. Sparks, "Guidance on Interoperation
              and Implementation Reports for Advancement to Draft
              Standard", BCP 9, RFC 5657, September 2009.

   [RFC3921]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Instant Messaging and Presence",
              RFC 3921, October 2004.

   [SASL]     Melnikov, A. and K. Zeilenga, "Simple Authentication and
              Security Layer (SASL)", RFC 4422, June 2006.

   [TLS]      Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [URI]      Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [XEP-0016]
              Millard, P. and P. Saint-Andre, "Privacy Lists", XSF
              XEP 0016, February 2007.

   [XEP-0045]
              Saint-Andre, P., "Multi-User Chat", XSF XEP 0045,
              July 2008.

   [XEP-0054]
              Saint-Andre, P., "vcard-temp", XSF XEP 0054, July 2008.

   [XEP-0071]



Saint-Andre              Expires October 2, 2010               [Page 89]

Internet-Draft                   XMPP IM                      March 2010


              Saint-Andre, P., "XHTML-IM", XSF XEP 0071, September 2008.

   [XEP-0115]
              Hildebrand, J., Saint-Andre, P., and R. Troncon, "Entity
              Capabilities", XSF XEP 0115, February 2008.

   [XEP-0147]
              Saint-Andre, P., "XMPP URI Scheme Query Components", XSF
              XEP 0147, September 2006.

   [XEP-0160]
              Saint-Andre, P., "Best Practices for Handling Offline
              Messages", XSF XEP 0160, January 2006.

   [XEP-0191]
              Saint-Andre, P., "Simple Communications Blocking", XSF
              XEP 0191, February 2007.

   [XEP-0201]
              Saint-Andre, P., Paterson, I., and K. Smith, "Best
              Practices for Message Threads", XSF XEP 0201,
              February 2008.

   [XEP-0237]
              Saint-Andre, P. and D. Cridland, "Roster Versioning", XSF
              XEP 0237, May 2009.

   [XML-SCHEMA]
              Thompson, H., Maloney, M., Mendelsohn, N., and D. Beech,
              "XML Schema Part 1: Structures Second Edition", World Wide
              Web Consortium Recommendation REC-xmlschema-1-20041028,
              October 2004,
              <http://www.w3.org/TR/2004/REC-xmlschema-1-20041028>.

   [VCARD]    Dawson, F. and T. Howes, "vCard MIME Directory Profile",
              RFC 2426, September 1998.


Appendix A.  Subscription States

   This section provides detailed information about subscription states
   and server processing of subscription-related presence stanzas (i.e.,
   presence stanzas of type "subscribe", "subscribed", "unsubscribe",
   and "unsubscribed").







Saint-Andre              Expires October 2, 2010               [Page 90]

Internet-Draft                   XMPP IM                      March 2010


A.1.  Defined States

   There are four primary subscription states (note: these states are
   described from the perspective of the user, not the contact):

   o  None -- the user does not have a subscription to the contact's
      presence, and the contact does not have a subscription to the
      user's presence
   o  To -- the user has a subscription to the contact's presence, but
      the contact does not have a subscription to the user's presence
   o  From -- the contact has a subscription to the user's presence, but
      the user does not have a subscription to the contact's presence
   o  Both -- both the user and the contact have subscriptions to each
      other's presence (i.e., the union of 'from' and 'to')

   These states are supplemented by various pending sub-states to yield
   nine possible subscription states:

   1.  "None" = contact and user are not subscribed to each other, and
       neither has requested a subscription from the other; this is
       reflected in the user's roster by subscription='none'
   2.  "None + Pending Out" = contact and user are not subscribed to
       each other, and user has sent contact a subscription request but
       contact has not replied yet; this is reflected in the user's
       roster by subscription='none' and ask='subscribe'
   3.  "None + Pending In" = contact and user are not subscribed to each
       other, and contact has sent user a subscription request but user
       has not replied yet; this state might or might not be reflected
       in the user's roster, as follows: if the user has created a
       roster item for the contact then the server MUST maintain that
       roster item and also note the existence of the inbound presence
       subscription request, whereas if the user has not created a
       roster item for the contact then the user's server MUST note the
       existence of the inbound presence subscription request but MUST
       NOT create a roster item for the contact (instead, the server
       MUST wait until the user has approved the subscription request
       before adding the contact to the user's roster).
   4.  "None + Pending Out+In" = contact and user are not subscribed to
       each other, contact has sent user a subscription request but user
       has not replied yet, and user has sent contact a subscription
       request but contact has not replied yet; this is reflected in the
       user's roster by subscription='none' and ask='subscribe'
   5.  "To" = user is subscribed to contact (one-way); this is reflected
       in the user's roster by subscription='to'
   6.  "To + Pending In" = user is subscribed to contact, and contact
       has sent user a subscription request but user has not replied
       yet; this is reflected in the user's roster by subscription='to'




Saint-Andre              Expires October 2, 2010               [Page 91]

Internet-Draft                   XMPP IM                      March 2010


   7.  "From" = contact is subscribed to user (one-way); this is
       reflected in the user's roster by subscription='from'
   8.  "From + Pending Out" = contact is subscribed to user, and user
       has sent contact a subscription request but contact has not
       replied yet; this is reflected in the user's roster by
       subscription='from' and ask='subscribe'
   9.  "Both" = user and contact are subscribed to each other (two-way);
       this is reflected in the user's roster by subscription='both'

A.2.  Server Processing of Outbound Presence Subscription Stanzas

   Outbound presence subscription stanzas enable the user to manage his
   or her subscription to the contact's presence (via the "subscribe"
   and "unsubscribe" types), and to manage the contact's access to the
   user's presence (via the "subscribed" and "unsubscribed" types).

   The following rules apply to outbound routing of the stanza as well
   as changes to the user's roster.

      Note: The rules for server processing of outbound presence
      subscription stanzas are described from the perspective of the
      user, not the contact.  In addition, "S.N." stands for SHOULD NOT.

A.2.1.  Subscribe

   Table 1: Processing of outbound "subscribe" stanzas

   +-----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
   +-----------------------------------------------------------------+
   |  "None"                  |  MUST    |  "None + Pending Out"     |
   |  "None + Pending Out"    |  MUST    |  no state change          |
   |  "None + Pending In"     |  MUST    |  "None + Pending Out+In"  |
   |  "None + Pending Out+In" |  MUST    |  no state change          |
   |  "To"                    |  MUST    |  no state change          |
   |  "To + Pending In"       |  MUST    |  no state change          |
   |  "From"                  |  MUST    |  "From + Pending Out"     |
   |  "From + Pending Out"    |  MUST    |  no state change          |
   |  "Both"                  |  MUST    |  no state change          |
   +-----------------------------------------------------------------+

      Note: A state change to "pending out" includes setting the 'ask'
      flag to a value of "subscribe" in the user's roster.








Saint-Andre              Expires October 2, 2010               [Page 92]

Internet-Draft                   XMPP IM                      March 2010


A.2.2.  Unsubscribe

   Table 2: Processing of outbound "unsubscribe" stanzas

   +-----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
   +-----------------------------------------------------------------+
   |  "None"                  |  MUST    |  no state change          |
   |  "None + Pending Out"    |  MUST    |  "None"                   |
   |  "None + Pending In"     |  MUST    |  no state change          |
   |  "None + Pending Out+In" |  MUST    |  "None + Pending In"      |
   |  "To"                    |  MUST    |  "None"                   |
   |  "To + Pending In"       |  MUST    |  "None + Pending In"      |
   |  "From"                  |  MUST    |  no state change          |
   |  "From + Pending Out"    |  MUST    |  "From"                   |
   |  "Both"                  |  MUST    |  "From"                   |
   +-----------------------------------------------------------------+

A.2.3.  Subscribed

   Table 3: Processing of outbound "subscribed" stanzas

   +-----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
   +-----------------------------------------------------------------+
   |  "None"                  |  S.N.    |  no state change [1]      |
   |  "None + Pending Out"    |  S.N.    |  no state change          |
   |  "None + Pending In"     |  MUST    |  "From"                   |
   |  "None + Pending Out+In" |  MUST    |  "From + Pending Out"     |
   |  "To"                    |  S.N.    |  no state change          |
   |  "To + Pending In"       |  MUST    |  "Both"                   |
   |  "From"                  |  S.N.    |  no state change          |
   |  "From + Pending Out"    |  S.N.    |  no state change          |
   |  "Both"                  |  S.N.    |  no state change          |
   +-----------------------------------------------------------------+

   [1] A server MAY note the fact that the user wishes to allow the
   contact to be subscribed to the user's presence and automatically
   approve any subscription request received from the contact; if it
   does so, upon the receiving presence stanza of type "subscribed" from
   the user's client it MUST add a roster item for the contact to the
   user's roster and set the 'ask' flag to a value of "subscribed".
   However, the user's server still SHOULD NOT route the presence stanza
   of type "subscribed" to the contact.  This optional functionality
   applies only if the contact is not already in the user's roster or if
   the contact is in the user's roster with a state of "None" (not
   including a state of "None + Pending Out").




Saint-Andre              Expires October 2, 2010               [Page 93]

Internet-Draft                   XMPP IM                      March 2010


A.2.4.  Unsubscribed

   Table 4: Processing of outbound "unsubscribed" stanzas

   +-----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
   +-----------------------------------------------------------------+
   |  "None"                  |  S.N.    |  no state change          |
   |  "None + Pending Out"    |  S.N.    |  no state change          |
   |  "None + Pending In"     |  MUST    |  "None"                   |
   |  "None + Pending Out+In" |  MUST    |  "None + Pending Out"     |
   |  "To"                    |  S.N.    |  no state change          |
   |  "To + Pending In"       |  MUST    |  "To"                     |
   |  "From"                  |  MUST    |  "None"                   |
   |  "From + Pending Out"    |  MUST    |  "None + Pending Out"     |
   |  "Both"                  |  MUST    |  "To"                     |
   +-----------------------------------------------------------------+

A.3.  Server Processing of Inbound Presence Subscription Stanzas

   Inbound presence subscription stanzas request a subscription-related
   action from the user (via the "subscribe" type), inform the user of
   subscription-related actions taken by the contact (via the
   "unsubscribe" type), or enable the user to manage the contact's
   access to the user's presence information (via the "subscribed" and
   "unsubscribed" types).

   The following rules apply to delivery of the inbound stanza as well
   as changes to the user's roster.

      Note: The rules for server processing of inbound presence
      subscription stanzas are described from the perspective of the
      user, not the contact.  In addition, "S.N." stands for SHOULD NOT.


















Saint-Andre              Expires October 2, 2010               [Page 94]

Internet-Draft                   XMPP IM                      March 2010


A.3.1.  Subscribe

   Table 5: Processing of inbound "subscribe" stanzas

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  MUST [1]  |  "None + Pending In"     |
   |  "None + Pending Out"    |  MUST      |  "None + Pending Out+In" |
   |  "None + Pending In"     |  S.N.      |  no state change         |
   |  "None + Pending Out+In" |  S.N.      |  no state change         |
   |  "To"                    |  MUST      |  "To + Pending In"       |
   |  "To + Pending In"       |  S.N.      |  no state change         |
   |  "From"                  |  S.N. [2]  |  no state change         |
   |  "From + Pending Out"    |  S.N. [2]  |  no state change         |
   |  "Both"                  |  S.N. [2]  |  no state change         |
   +------------------------------------------------------------------+

   [1] If the user previously sent presence of type "subscribed" as
   described under Appendix A.2.3, then the server MAY auto-reply with
   "subscribed" and change the state to "From" rather than "None +
   Pending In".

   [2] Server SHOULD auto-reply with "subscribed".

A.3.2.  Unsubscribe

   When the user's server receives a presence stanza of type
   "unsubscribe" for the user from the contact, if the stanza results in
   a subscription state change from the user's perspective then the
   user's server MUST change the state, MUST deliver the presence stanza
   from the contact to the user, and SHOULD auto-reply by sending a
   presence stanza of type "unsubscribed" to the contact on behalf of
   the user.  Otherwise the user's server MUST NOT change the state and
   (because there is no stage change) SHOULD NOT deliver the stanza.
   These rules are summarized in the following table.















Saint-Andre              Expires October 2, 2010               [Page 95]

Internet-Draft                   XMPP IM                      March 2010


   Table 6: Processing of inbound "unsubscribe" stanzas

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  S.N.      |  no state change         |
   |  "None + Pending Out"    |  S.N.      |  no state change         |
   |  "None + Pending In"     |  MUST [1]  |  "None"                  |
   |  "None + Pending Out+In" |  MUST [1]  |  "None + Pending Out"    |
   |  "To"                    |  S.N.      |  no state change         |
   |  "To + Pending In"       |  MUST [1]  |  "To"                    |
   |  "From"                  |  MUST [1]  |  "None"                  |
   |  "From + Pending Out"    |  MUST [1]  |  "None + Pending Out     |
   |  "Both"                  |  MUST [1]  |  "To"                    |
   +------------------------------------------------------------------+

   [1] Server SHOULD auto-reply with "unsubscribed".

A.3.3.  Subscribed

   When the user's server receives a presence stanza of type
   "subscribed" for the user from the contact, if there is no pending
   outbound request for access to the contact's presence information,
   then it MUST NOT change the subscription state and (because there is
   no state change) SHOULD NOT deliver the stanza to the user.  If there
   is a pending outbound request for access to the contact's presence
   information and the inbound presence stanza of type "subscribed"
   results in a subscription state change, then the user's server MUST
   change the subscription state and MUST deliver the stanza to the
   user.  If the user already has access to the contact's presence
   information, the inbound presence stanza of type "subscribed" does
   not result in a subscription state change; therefore the user's
   server MUST NOT change the subscription state and (because there is
   no state change) SHOULD NOT deliver the stanza to the user.  These
   rules are summarized in the following table.
















Saint-Andre              Expires October 2, 2010               [Page 96]

Internet-Draft                   XMPP IM                      March 2010


   Table 7: Processing of inbound "subscribed" stanzas

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  S.N.      |  no state change         |
   |  "None + Pending Out"    |  MUST      |  "To"                    |
   |  "None + Pending In"     |  S.N.      |  no state change         |
   |  "None + Pending Out+In" |  MUST      |  "To + Pending In"       |
   |  "To"                    |  S.N.      |  no state change         |
   |  "To + Pending In"       |  S.N.      |  no state change         |
   |  "From"                  |  S.N.      |  no state change         |
   |  "From + Pending Out"    |  MUST      |  "Both"                  |
   |  "Both"                  |  S.N.      |  no state change         |
   +------------------------------------------------------------------+

A.3.4.  Unsubscribed

   When the user's server receives a presence stanza of type
   "unsubscribed" for the user from the contact, if there is a pending
   outbound request for access to the contact's presence information or
   if the user currently has access to the contact's presence
   information, then the user's server MUST change the subscription
   state and MUST deliver the stanza to the user.  Otherwise, the user's
   server MUST NOT change the subscription state and (because there is
   no state change) SHOULD NOT deliver the stanza.  These rules are
   summarized in the following table.

   Table 8: Processing of inbound "unsubscribed" stanzas

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  S.N.      |  no state change         |
   |  "None + Pending Out"    |  MUST      |  "None"                  |
   |  "None + Pending In"     |  S.N.      |  no state change         |
   |  "None + Pending Out+In" |  MUST      |  "None + Pending In"     |
   |  "To"                    |  MUST      |  "None"                  |
   |  "To + Pending In"       |  MUST      |  "None + Pending In"     |
   |  "From"                  |  S.N.      |  no state change         |
   |  "From + Pending Out"    |  MUST      |  "From"                  |
   |  "Both"                  |  MUST      |  "From"                  |
   +------------------------------------------------------------------+








Saint-Andre              Expires October 2, 2010               [Page 97]

Internet-Draft                   XMPP IM                      March 2010


Appendix B.  Blocking Communication

   Sections 2.3.5 and 5.4.10 of [IMP-REQS] require that a compliant
   instant messaging and presence technology must enable a user to block
   communications from selected users.  Protocols for doing so are
   specified in [XEP-0016] and [XEP-0191].


Appendix C.  vCards

   Sections 3.1.3 and 4.1.4 of [IMP-REQS] require that it be possible to
   retrieve out-of-band contact information for other users (e.g.,
   telephone number or email address).  An XML representation of the
   vCard specification defined in RFC 2426 [VCARD] is in common use
   within the Jabber community to provide such information but is out of
   scope for this specification (documentation of this protocol is
   contained in [XEP-0054]).


Appendix D.  XML Schemas

   Because validation of XML streams and stanzas is optional, the
   following XML schemas are provided for descriptive purposes only.
   These schemas are not normative.

   The following schemas formally define various XML namespaces used in
   the core XMPP protocols, in conformance with [XML-SCHEMA].  For
   schemas defining namespaces for XML streams and other core aspects of
   XMPP, refer to [XMPP-CORE].

D.1.  jabber:client

   <?xml version='1.0' encoding='UTF-8'?>

   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:client'
       xmlns='jabber:client'
       elementFormDefault='qualified'>

     <xs:import
         namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/>

     <xs:element name='message'>
        <xs:complexType>
           <xs:sequence>
             <xs:choice minOccurs='0' maxOccurs='unbounded'>
               <xs:element ref='subject'/>



Saint-Andre              Expires October 2, 2010               [Page 98]

Internet-Draft                   XMPP IM                      March 2010


               <xs:element ref='body'/>
               <xs:element ref='thread'/>
             </xs:choice>
             <xs:any     namespace='##other'
                         minOccurs='0'
                         maxOccurs='unbounded'/>
             <xs:element ref='error'
                         minOccurs='0'/>
           </xs:sequence>
           <xs:attribute name='from'
                         type='xs:string'
                         use='optional'/>
           <xs:attribute name='id'
                         type='xs:NMTOKEN'
                         use='optional'/>
           <xs:attribute name='to'
                         type='xs:string'
                         use='optional'/>
           <xs:attribute name='type'
                         use='optional'
                         default='normal'>
             <xs:simpleType>
               <xs:restriction base='xs:NCName'>
                 <xs:enumeration value='chat'/>
                 <xs:enumeration value='error'/>
                 <xs:enumeration value='groupchat'/>
                 <xs:enumeration value='headline'/>
                 <xs:enumeration value='normal'/>
               </xs:restriction>
             </xs:simpleType>
           </xs:attribute>
           <xs:attribute ref='xml:lang' use='optional'/>
        </xs:complexType>
     </xs:element>

     <xs:element name='body'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:string'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='subject'>
       <xs:complexType>
         <xs:simpleContent>



Saint-Andre              Expires October 2, 2010               [Page 99]

Internet-Draft                   XMPP IM                      March 2010


           <xs:extension base='xs:string'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='thread'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:NMTOKEN'>
             <xs:attribute name='parent'
                           type='xs:NMTOKEN'
                           use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='presence'>
       <xs:complexType>
         <xs:sequence>
           <xs:choice minOccurs='0' maxOccurs='unbounded'>
             <xs:element ref='show'/>
             <xs:element ref='status'/>
             <xs:element ref='priority'/>
           </xs:choice>
           <xs:any     namespace='##other'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
           <xs:element ref='error'
                       minOccurs='0'/>
         </xs:sequence>
         <xs:attribute name='from'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='optional'/>
         <xs:attribute name='to'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='type' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='error'/>
               <xs:enumeration value='probe'/>
               <xs:enumeration value='subscribe'/>



Saint-Andre              Expires October 2, 2010              [Page 100]

Internet-Draft                   XMPP IM                      March 2010


               <xs:enumeration value='subscribed'/>
               <xs:enumeration value='unavailable'/>
               <xs:enumeration value='unsubscribe'/>
               <xs:enumeration value='unsubscribed'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='show'>
       <xs:simpleType>
         <xs:restriction base='xs:NCName'>
           <xs:enumeration value='away'/>
           <xs:enumeration value='chat'/>
           <xs:enumeration value='dnd'/>
           <xs:enumeration value='xa'/>
         </xs:restriction>
       </xs:simpleType>
     </xs:element>

     <xs:element name='status'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='string1024'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:simpleType name='string1024'>
       <xs:restriction base='xs:string'>
         <xs:minLength value='1'/>
         <xs:maxLength value='1024'/>
       </xs:restriction>
     </xs:simpleType>

     <xs:element name='priority' type='xs:byte'/>

     <xs:element name='iq'>
       <xs:complexType>
         <xs:sequence>
           <xs:any     namespace='##other'
                       minOccurs='0'/>
           <xs:element ref='error'
                       minOccurs='0'/>



Saint-Andre              Expires October 2, 2010              [Page 101]

Internet-Draft                   XMPP IM                      March 2010


         </xs:sequence>
         <xs:attribute name='from'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='required'/>
         <xs:attribute name='to'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='type' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='error'/>
               <xs:enumeration value='get'/>
               <xs:enumeration value='result'/>
               <xs:enumeration value='set'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='error'>
       <xs:complexType>
         <xs:sequence xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'>
           <xs:group ref='err:stanzaErrorGroup'/>
           <xs:element ref='err:text'
                       minOccurs='0'/>
         </xs:sequence>
         <xs:attribute name='type' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='auth'/>
               <xs:enumeration value='cancel'/>
               <xs:enumeration value='continue'/>
               <xs:enumeration value='modify'/>
               <xs:enumeration value='wait'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>
     </xs:element>

   </xs:schema>

D.2.  jabber:server



Saint-Andre              Expires October 2, 2010              [Page 102]

Internet-Draft                   XMPP IM                      March 2010


   <?xml version='1.0' encoding='UTF-8'?>

   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:server'
       xmlns='jabber:server'
       elementFormDefault='qualified'>

     <xs:import
         namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/>

     <xs:element name='message'>
        <xs:complexType>
           <xs:sequence>
             <xs:choice minOccurs='0' maxOccurs='unbounded'>
               <xs:element ref='subject'/>
               <xs:element ref='body'/>
               <xs:element ref='thread'/>
             </xs:choice>
             <xs:any namespace='##other'
                     minOccurs='0'
                     maxOccurs='unbounded'/>
             <xs:element ref='error'
                         minOccurs='0'/>
           </xs:sequence>
           <xs:attribute name='from'
                         type='xs:string'
                         use='required'/>
           <xs:attribute name='id'
                         type='xs:NMTOKEN'
                         use='optional'/>
           <xs:attribute name='to'
                         type='xs:string'
                         use='required'/>
           <xs:attribute name='type'
                         use='optional'
                         default='normal'>
             <xs:simpleType>
               <xs:restriction base='xs:NCName'>
                 <xs:enumeration value='chat'/>
                 <xs:enumeration value='error'/>
                 <xs:enumeration value='groupchat'/>
                 <xs:enumeration value='headline'/>
                 <xs:enumeration value='normal'/>
               </xs:restriction>
             </xs:simpleType>
           </xs:attribute>
           <xs:attribute ref='xml:lang' use='optional'/>



Saint-Andre              Expires October 2, 2010              [Page 103]

Internet-Draft                   XMPP IM                      March 2010


        </xs:complexType>
     </xs:element>

     <xs:element name='body'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:string'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='subject'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:string'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='thread'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:NMTOKEN'>
             <xs:attribute name='parent'
                           type='xs:NMTOKEN'
                           use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='subject'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:NMTOKEN'>
             <xs:attribute name='parent'
                           type='xs:NMTOKEN'
                           use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='presence'>



Saint-Andre              Expires October 2, 2010              [Page 104]

Internet-Draft                   XMPP IM                      March 2010


       <xs:complexType>
         <xs:sequence>
           <xs:choice minOccurs='0' maxOccurs='unbounded'>
             <xs:element ref='show'/>
             <xs:element ref='status'/>
             <xs:element ref='priority'/>
           </xs:choice>
           <xs:any     namespace='##other'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
           <xs:element ref='error'
                       minOccurs='0'/>
         </xs:sequence>
         <xs:attribute name='from'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='optional'/>
         <xs:attribute name='to'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='type' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='error'/>
               <xs:enumeration value='probe'/>
               <xs:enumeration value='subscribe'/>
               <xs:enumeration value='subscribed'/>
               <xs:enumeration value='unavailable'/>
               <xs:enumeration value='unsubscribe'/>
               <xs:enumeration value='unsubscribed'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='show'>
       <xs:simpleType>
         <xs:restriction base='xs:NCName'>
           <xs:enumeration value='away'/>
           <xs:enumeration value='chat'/>
           <xs:enumeration value='dnd'/>
           <xs:enumeration value='xa'/>
         </xs:restriction>
       </xs:simpleType>



Saint-Andre              Expires October 2, 2010              [Page 105]

Internet-Draft                   XMPP IM                      March 2010


     </xs:element>

     <xs:element name='status'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='string1024'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:simpleType name='string1024'>
       <xs:restriction base='xs:string'>
         <xs:minLength value='1'/>
         <xs:maxLength value='1024'/>
       </xs:restriction>
     </xs:simpleType>

     <xs:element name='priority' type='xs:byte' default='0'/>

     <xs:element name='iq'>
       <xs:complexType>
         <xs:sequence>
           <xs:any namespace='##other'
                   minOccurs='0'/>
           <xs:element ref='error'
                       minOccurs='0'/>
         </xs:sequence>
         <xs:attribute name='from'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='required'/>
         <xs:attribute name='to'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='type' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='error'/>
               <xs:enumeration value='get'/>
               <xs:enumeration value='result'/>
               <xs:enumeration value='set'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>



Saint-Andre              Expires October 2, 2010              [Page 106]

Internet-Draft                   XMPP IM                      March 2010


         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='error'>
       <xs:complexType>
         <xs:sequence xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'>
           <xs:group ref='err:stanzaErrorGroup'/>
           <xs:element ref='err:text'
                       minOccurs='0'/>
         </xs:sequence>
         <xs:attribute name='type' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='auth'/>
               <xs:enumeration value='cancel'/>
               <xs:enumeration value='continue'/>
               <xs:enumeration value='modify'/>
               <xs:enumeration value='wait'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>
     </xs:element>

   </xs:schema>

D.3.  jabber:iq:roster

   <?xml version='1.0' encoding='UTF-8'?>

   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:iq:roster'
       xmlns='jabber:iq:roster'
       elementFormDefault='qualified'>

     <xs:element name='query'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='item'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
         </xs:sequence>
         <xs:attribute name='ver'
                       type='xs:string'
                       use='optional'/>
       </xs:complexType>



Saint-Andre              Expires October 2, 2010              [Page 107]

Internet-Draft                   XMPP IM                      March 2010


     </xs:element>

     <xs:element name='item'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='group'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
         </xs:sequence>
         <xs:attribute name='ask' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='subscribe'/>
               <xs:enumeration value='subscribed'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute name='jid'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='name'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='subscription'
                       use='optional'
                       default='none'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='both'/>
               <xs:enumeration value='from'/>
               <xs:enumeration value='none'/>
               <xs:enumeration value='remove'/>
               <xs:enumeration value='to'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>
     </xs:element>

     <xs:element name='group' type='xs:string'/>

   </xs:schema>


Appendix E.  Differences From RFC 3921

   Based on consensus derived from implementation and deployment
   experience as well as formal interoperability testing, the following



Saint-Andre              Expires October 2, 2010              [Page 108]

Internet-Draft                   XMPP IM                      March 2010


   substantive modifications were made from RFC 3921.

   o  The protocol for session establishment was determined to be
      unnecessary and therefore the content previously defined in
      Section 3 of RFC 3921 was removed.  However, for the sake of
      backward-compatibility server implementations are encouraged to
      advertise support for the feature, even though session
      establishment is a "no-op".
   o  In order to more seamlessly repair lack of synchronization in
      subscription states between rosters located at different servers,
      clarified and modified error handling related to presence
      subscription requests, presence probes and presence notifications.
   o  Explicitly specified that a server is allowed to deliver a message
      stanza of type "chat" or "normal" to all resources.
   o  Added optional versioning of roster information to save bandwidth
      in cases where the roster has not changed (or has changed very
      little) between sessions; the relevant protocol interactions were
      originally described in [XEP-0237].
   o  Added optional server support for pre-approved presence
      subscriptions via presence stanzas of type "subscribed" and the
      optional "subscribed" value for the 'ask' flag.
   o  Added optional 'parent' attribute to <thread/> element
   o  Moved the protocol for communications blocking (specified in
      Section 10 of RFC 3921) back to [XEP-0016], from which it was
      originally taken.

   In addition, numerous changes of an editorial nature were made in
   order to more fully specify and clearly explain the protocols,
   including the following.

   o  Recommended returning presence unavailable in response to probes.
   o  Clarified handling of presence probes sent to full JIDs.
   o  Explicitly specified that the default value for the presence
      <priority/> element is zero.


Appendix F.  Copying Conditions

   Regarding this entire document or any portion of it, the author makes
   no guarantees and is not responsible for any damage resulting from
   its use.  The author grants irrevocable permission to anyone to use,
   modify, and distribute it in any way that does not diminish the
   rights of anyone else to use, modify, and distribute it, provided
   that redistributed derivative works do not contain misleading author
   or version information.  Derivative works need not be licensed under
   similar terms.





Saint-Andre              Expires October 2, 2010              [Page 109]

Internet-Draft                   XMPP IM                      March 2010


Index

   A
      Available Resource  44

   C
      Chat Session  62
      Contact  29

   D
      Directed Presence  44

   I
      Initial Presence  45

   O
      Offline Message Storage  80

   P
      Presence  7
      Presence Broadcast  44
      Presence Probe  46
      Presence Session  44
      Presence Subscription  29

   R
      Roster  7
      Roster Get  12
      Roster Push  13
      Roster Result  13
      Roster Set  12

   S
      Subscription Request  30

   U
      Unavailable Presence  53


Author's Address

   Peter Saint-Andre
   Cisco

   Email: psaintan@cisco.com






Saint-Andre              Expires October 2, 2010              [Page 110]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/